I'm 15 In love with a 19 year old girl

Sure; I don't see any reason why not.

The sex issue is a big one, though. Regardless of how deeply committed either of you are to your faith, you may still find yourselves tempted. You are under 18, and that is going to be problematic until you cross the 18 threshold.

Also, nobody here is going to judge you for liking someone who is 'big'. We all need human contact, regardless of our clothing sizes. Go get 'em, Tiger.