Your fastball should be slightly faster off a mound, 1-3 mph sounds about right.
As for your height, don't worry about it. Why worry about something you can't control? Freshman year, I was 15, and I was 5'7'' 140 and made the freshman team. Sophomore year, I was 16, and I was 5'8'' 155. I'm not too much bigger than you. The thing with me is my parents are both pretty short, my dad's 5'7'' and my mom's 5'6''. Maybe you'll grow later, but you'll have to wait to find out. Just remember, don't worry about something you can't control. You should be worrying about things you can control, like how hard you're willing to work.