I'm about to return after a 3 months hiatus due to a hip problem. I am now practicing with 14 lb. balls and will use them until I feel it's safe to return to 15 lb.balls.
The major difference between 15 and 14 lb. balls is not in hitting or carry power but in drilling to account for your release/delivery with the different RGs and different differentials in 14 lb. balls vs. 15 lb. balls.
You have to investigate each ball separately because some have the same RG, sometimes the 14 has a lower RG, and sometimes it has a higher RG. The same is true for the differential. You and your driller have to account for those differences in the drilling (to get a similar reaction, that is).
Two other differences are the rev rate and the ball speed. Both might go up but to different degrees. You should test drillings/surfaces and results with a 2 used balls to see what happens.
