16hh really isn't all that big. my barn is basically full of 17hh horses & up. if you are still growing, go for the bigger horse, if you're done growing, and you're on the shorter side, get the smaller one. also, the difference between a 15.2hh horse & a 16hh horse are two inches, which really isn't much of a difference.
Depends on the type of horse your wanting to get. Also how tall you are. I'd say go for the 15.2 horse of your shorter but the 16 horse if your taller. Also try them out and see which one fits you better.
I think there may be less problems on a slightly bigger horse because you know if you are still growing than that's the better choice but if your not, the 15.2 may be a little small but more permanent you see what I mean?