As soon as the generating set of a Cayley graph of a group $G$ is a union of conjugacy classes of $G$, the graph lives in the commutative association scheme of these classes, where the multiplication is determined by the character table of $G$. Thus things like diameter, eigenvalues, can be determined from the character table, although this is not necessarily trivial.
Just for fun, I computed the eigenvalues of this graph for $G=A_n$, $n=15$, and they are all integers. Not sure if this is easy to explain...