More often than not, it's because 15lbs seem to have the higher RG and Differential ratings. It appears that the change from 16-15 has zero effect on pin carry or hitting power with new core/coverstock technology, so dropping a pound had no negative effects. It's easier on your body, your arm, some people pick up a little speed, as well as a few more revs, less fatigue through long sets of more than 3-6 or even 10 game series. 1lb less makes it easier to stay under the ball, keep your wrist and fingers in a stronger position. Sometimes, 1 lb higher or lower, can be the key to fix a timing issues. More relaxed back swing, possible a higher back swing because of the relaxing, less squeezing and even more carry and pin reaction. Some people dropped to 15, just because of the access to a lot more used ball options, lol.
But these are just a few reasons based on what I've heard/read from people, and my own experience. Not to be taken as 100% proven facts.
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Mega Friction 278
Virtual Gravity 272
Twisted Fury 268
The Sauce 255
Rogue Cell
FS/FT Black Widow Solid $30
FS/FT Kinetic Energy $25
