I am very comfortable riding 15.1-15.2. In fact, that is what I am used too. However, I FIT best on horses about 16.2-16.3. Before I transferred down to So. Miss., I was riding a 16.2 Appy, and a 16.2 Oldenberg/Warmblood cross. I have never heard my instructor gush so much about how well I fit a horse before.
16.2 seems to be my number. I'm 5'11" short.