I tried 15 lb about 2 years ago. I did not have any problems with my timing. However I did not carry as well. I ended up going back to 16 lb to increase my carry. In my opinion, the more you hook the ball, the more likely 15 lb will work for you. The straighter you throw the ball, the more likely a 16 lb will work for you.
If you can pick up a 15 lb for not much money, do it. Unless you try it, you will always wonder if 15 lb is right for you.