I did want to see the behavior of specific forms of low discriminant from Nipp's tables, as Jeremy briefly indicated in an email. To get $r(n) \geq 15 \sigma(n)$ we seem to need discriminant $d \leq 21.$ To get $r(n) \geq 20 \sigma(n)$ we seem to need discriminant $d = 4,5.$ Then  discriminant $5$ achieves the ratio $24.$ For $d=5,$ with prime $p \equiv \pm 2 \pmod 5,$ we get
$$  r(p) = 30 (p-1) = 30 \; \sigma(p)  \cdot \left( \frac{p-1}{p+1} \right) $$  




      d  4 record ratio  24 number  1       sigma  1   reps  24
      d  5 record ratio  29.5652173913043 number  137       sigma  138   reps  4080
      d  8 record ratio  17.76 number  149       sigma  150   reps  2664
      d  9 record ratio  12 number  1       sigma  1   reps  12
      d  12 record ratio  19.4117647058824 number  67       sigma  68   reps  1320
      d  12 record ratio  19.7333333333333 number  149       sigma  150   reps  2960
      d  13 record ratio  13.8133333333333 number  149       sigma  150   reps  2072
      d  16 record ratio  8 number  1       sigma  1   reps  8
      d  16 record ratio  12 number  1       sigma  1   reps  12
      d  17 record ratio  8.87142857142857 number  139       sigma  140   reps  1242
      d  20 record ratio  17.7391304347826 number  137       sigma  138   reps  2448
      d  20 record ratio  13.6216216216216 number  146       sigma  222   reps  3024
      d  20 record ratio  11.8260869565217 number  137       sigma  138   reps  1632
      d  21 record ratio  15.7866666666667 number  149       sigma  150   reps  2368
      d  21 record ratio  15.7714285714286 number  139       sigma  140   reps  2208
      d  24 record ratio  11.8125 number  127       sigma  128   reps  1512
      d  24 record ratio  12 number  1       sigma  1   reps  12
      d  24 record ratio  11.8260869565217 number  137       sigma  138   reps  1632
      d  25 record ratio  6 number  1       sigma  1   reps  6
      d  28 record ratio  9.80392156862745 number  101       sigma  102   reps  1000
      d  28 record ratio  12 number  1       sigma  1   reps  12
      d  28 record ratio  9.84375 number  127       sigma  128   reps  1260
      d  29 record ratio  10 number  5       sigma  6   reps  60
      d  29 record ratio  12 number  1       sigma  1   reps  12
      d  32 record ratio  9.86666666666667 number  149       sigma  150   reps  1480
      d  32 record ratio  11.84 number  149       sigma  150   reps  1776
      d  32 record ratio  12 number  1       sigma  1   reps  12
      d  32 record ratio  8.41176470588235 number  134       sigma  204   reps  1716
      d  32 record ratio  11.8285714285714 number  139       sigma  140   reps  1656
      d  33 record ratio  8 number  1       sigma  1   reps  8
      d  33 record ratio  7.88571428571429 number  139       sigma  140   reps  1104
      d  33 record ratio  7.88405797101449 number  137       sigma  138   reps  1088
      d  36 record ratio  12 number  1       sigma  1   reps  12
      d  36 record ratio  12 number  5       sigma  6   reps  72
      d  36 record ratio  8 number  1       sigma  1   reps  8
      d  36 record ratio  11.9504132231405 number  81       sigma  121   reps  1446
      d  36 record ratio  7.9843137254902 number  128       sigma  255   reps  2036
      d  37 record ratio  12 number  1       sigma  1   reps  12
      d  37 record ratio  7.5 number  3       sigma  4   reps  30
      d  40 record ratio  12 number  1       sigma  1   reps  12
      d  40 record ratio  7.71875 number  127       sigma  128   reps  988
      d  40 record ratio  7.92156862745098 number  101       sigma  102   reps  808
      d  40 record ratio  7.84 number  149       sigma  150   reps  1176
      d  41 record ratio  8 number  1       sigma  1   reps  8
      d  41 record ratio  5.33333333333333 number  2       sigma  3   reps  16
      d  44 record ratio  8.64 number  149       sigma  150   reps  1296
      d  44 record ratio  8.51612903225806 number  61       sigma  62   reps  528
      d  44 record ratio  12 number  1       sigma  1   reps  12
      d  44 record ratio  8.44444444444444 number  71       sigma  72   reps  608
      d  45 record ratio  11.8260869565217 number  137       sigma  138   reps  1632
      d  45 record ratio  12 number  1       sigma  1   reps  12
      d  45 record ratio  11.8125 number  127       sigma  128   reps  1512
      d  45 record ratio  11.5 number  141       sigma  192   reps  2208
      d  45 record ratio  11.8260869565217 number  137       sigma  138   reps  1632
      d  48 record ratio  11.84 number  149       sigma  150   reps  1776
      d  48 record ratio  9.86666666666667 number  149       sigma  150   reps  1480
      d  48 record ratio  9.86666666666667 number  149       sigma  150   reps  1480
      d  48 record ratio  12 number  1       sigma  1   reps  12
      d  48 record ratio  9.85714285714286 number  139       sigma  140   reps  1380
      d  48 record ratio  8.98765432098766 number  106       sigma  162   reps  1456
      d  48 record ratio  11.8285714285714 number  139       sigma  140   reps  1656
      d  48 record ratio  12 number  11       sigma  12   reps  144
      d  48 record ratio  9.05882352941176 number  134       sigma  204   reps  1848
      d  49 record ratio  4 number  1       sigma  1   reps  4
      d  52 record ratio  6.52941176470588 number  134       sigma  204   reps  1332
      d  52 record ratio  6.40740740740741 number  142       sigma  216   reps  1384
      d  52 record ratio  12 number  1       sigma  1   reps  12
      d  52 record ratio  8.3265306122449 number  97       sigma  98   reps  816
      d  52 record ratio  5.55102040816327 number  97       sigma  98   reps  544
      d  52 record ratio  6 number  1       sigma  1   reps  6
      d  53 record ratio  8.12903225806452 number  61       sigma  62   reps  504
      d  53 record ratio  12 number  1       sigma  1   reps  12
      d  53 record ratio  8 number  11       sigma  12   reps  96
      d  56 record ratio  8 number  1       sigma  1   reps  8
      d  56 record ratio  7.22222222222222 number  71       sigma  72   reps  520
      d  56 record ratio  7.46666666666667 number  89       sigma  90   reps  672
      d  56 record ratio  12 number  1       sigma  1   reps  12
      d  56 record ratio  7.15151515151515 number  131       sigma  132   reps  944
      d  57 record ratio  8 number  1       sigma  1   reps  8
      d  57 record ratio  5.66666666666667 number  149       sigma  150   reps  850
      d  57 record ratio  5.68421052631579 number  37       sigma  38   reps  216
      d  57 record ratio  6 number  1       sigma  1   reps  6
      d  60 record ratio  9.79591836734694 number  97       sigma  98   reps  960
      d  60 record ratio  12 number  1       sigma  1   reps  12
      d  60 record ratio  9.79591836734694 number  97       sigma  98   reps  960
      d  60 record ratio  9.86666666666667 number  149       sigma  150   reps  1480
      d  60 record ratio  9.86666666666667 number  149       sigma  150   reps  1480
      d  60 record ratio  9.85714285714286 number  139       sigma  140   reps  1380