I'm probably getting the 16's for my next pair. I ran in the 14's and then the 15's and have remained fairly injury free so I figure I won't mess with a good thing.
One weird thing with the 15's - my last pair seemed noticeably smaller than the previous two pairs. Same size, same width - but fit a little tighter than the previous two pairs. I wouldn't mind the toe box being a little roomier.