Is an easy proof of an interesting result worth publishing?

Probably not (but "probably" doesn't mean "certainly", so, as others said, ask your adviser).

The issue is that as a PhD student, your perspective on what counts as "interesting" and what counts as "easy" is likely to be different than the perspective of the sort of more experienced mathematicians who make up the intended readership of your prospective publication, and who would referee it. As one gains experience in mathematics, what one once regarded as "easy" will often get downgraded to "completely trivial" (and what one regarded as "somewhat nontrivial" gets downgraded to "easy", what one regarded as "hard" gets downgraded to "somewhat nontrivial", and so on). Similarly, what one has regarded as "interesting" as a PhD student will quite often later be revised to "mildly noteworthy" or even further to "not interesting".

Basically, this evolution in one's perception of how interesting/clever/publishable/etc one's ideas are is not only common and natural, but always points in the same direction. So if you think your result is easy now, just wait a few years...