Is it okay for two teenagers, me being 16 and her being 15, to get engaged?

So I'm in love with this girl and she's in love with me. Me and Cheyenne (the girl) were talking earlier and we told each other how much we love each other. I'm 16 and she's 15. We really want to be together. Currently we aren't just because we agreed we'd wait until we'd actually go on a real date. We don't want to say we're going out and not do anything. So then we were talking and she said that she thinks the namen Cheyenne Gillespie (Gillespie is my last name) has a very nice ring to it. I thought she was kidding at first, but then we talked more and she was dead serious. So after talking we decided we'd go out sometime and if we hit it off we won't be in relationship. We'd be engaged. I understand how that part is weird if it's the first date. So we agreed that we'd wait until at least her 18th birthday to get married. That way we got about at least 3 years to think it over. Is this the right thing we're doing? But please, don't say were not really in love. When I said I love girls in the past I had doubts about them. This one I have no doubts what so ever.