Depends how serious you are about her. I know you just started, but it does. If you're just loving around, well..
If you're loving around, then keep quiet. If you're just having legal, safe fun dating then I wouldn't worry about it. I wouldn't bring up her age until she turns 16 though because 16->18 isn't too bad but 15->18 sounds pretty bad.
However, long term, you gotta realize it's gonna suck. Even if you go to community college to be near her, and when you both graduate you go to the same college, the age gap is gonna be really hard when you turn 21.. and 22.. and 23..