We think all 15 year old girls are innocent, but they often aren't. And while I haven't seen a picture of her, there are also 15 year olds out there who look 21 and vice versa. This is one these cases where it's probably best not to judge without all the necessary information at hand.
I can see the benefits of a relationship. In any case you simply choose. Why bother with one if you're going to sleep around anyway. The drama would mess with my head. But I guess some people like drama.