Depends on your definition of 'simple', I guess.

My preference is to have all behaviours be explicit in the declared code, rather than implicit or as a side-effect. Much simpler to read and reason about the program.

Clarity over cleverness. To that end, I prefer this version over 'hiding' the mod 15 case for the sake of saving a line of code.

I also appreciate languages that warn (or better, require) that all cases are covered.