First, it is important to understand why 15 can be beneficial, or at least not a detriment compared to 16.  Many people think it is because the balls hit to hard, and that the lighter weight keeps the ball from overpowering the pocket.  Actually what has really happened is that their is so much friction, that higher ball speed is necessary to keep most peoples balls from burning off their rotational energy too early.  In addition, if you have a soft release ( Pete Weber example ) you can increase your rev rate and your ball speed.  These two factors cause 15 to hit just as hard or harder for most people on the predominant conditions we see today. 

Not too many people see any downside from going to 15.  If we ever see a situation where friction becomes a premium, rather than an excess, 16 could again become an advantage.