This all comes down to a matter of feel. 14, 15, and 16 will hit fine some better than others depending on the bowler. In other words, if it's too heavy, you may not have enough leverage, and vice-versa.
The wrist test that Ron mentions is a good way to see if a ball is too heavy for somebody. Once you get beyond the youth bowling, i.e., kids start to reach 120 pounds or so, the traditional "10% of body weight" no longer applies, i.e., you could be 130 throwing 15, you could be 180 throwing 14.
You want to be able to handle the weight, i.e., the wrist test, but you also want to be in control, i.e., not too light. If you feel too comfortable muscling the ball, it might simply be too light.
Temper this with the fact that when you first throw a lighter weight, it will certainly feel lighter. Be patient and you will get your timing back pretty quickly.
Just don't go back and forth. In other words, don't throw 14 one night and 15 another. Believe me, it will be tempting to pick up your "old" equipment on a night you feel off...
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