This whole post could have been 3 lines without losing any important information.
Date who you want and seeing as you share the same religious beliefs it should be easy. You're both too young (especially him) to even be thinking about marriage, cross that bridge when you get to it - if you get to it.
Also, at 17 I could never imagine dating a 15 year old but do you (and don't break any laws IYGM).