There are a dozen threads discussing the differences between 15# and 16# balls. Might be a good idea to find some of them.
As for feeling lighter or heavier, it's moot. 15# is 15#. Two balls that say 15# 3oz will weigh the same. Doesn't matter what core, cover, or filler is used. But an ill-fitting 15# might feel as heavy in the hand as a 16#.
SH