For a while, I had a combination of 16# and 15# equipment. It didn't seem to make much of a difference, and sometimes the weight difference was too great to feel comfortable adapting to. And whenever I'd leave a flat 10 with a 16# ball, I'd say to myself "heck, I can do that with a 15# ball.." So, at the beginning of this winter league season, I decided to go all 15# full time. I'm happy I made the switch. Another bonus with throwing 15# equipment is the resale factor. It's been much easier to unload no longer needed used balls that are 15# than 16#.
The standard rule of thumb still applies, though. If you're comfortable throwing 16# and are happy with the results, stay with it. There's no reason to change ball weight if you're having success with what you're using now.