Isn't 15 just the funnest ever? I don't want to lay it all on her age, but where she is developmentally could have a lot to do with her attitude about sports, or anything else for that matter. For one thing there frontal lobe hasn't developed fully and won't for quite a few years (around 5) and that limits her critical thinking skills. It's why she has no concept of how now relates to college or most cause and effect. If she makes boneheaded decisions, this is part of the reason. When she hit puberty the raging ammount of hormones added to that problem. They say a 10 yr. old has better decision making and critical thinking skills then a teenager, because teens are going through a kind of "brain dump" brought on my the hormones.
I say all that to say that maybe she is interested and in some part of her motivated, but maybe 5 years seems forever away and she just can't make the connection between training now and college 5 years from now. In her mind five years might as well be a million. She's got plenty of time but right now she just wants to lay back and relax. The problem is that we are always in the "right now" and that kind of thinking is a bad idea to entertain.
Call a local college athletics department and speak to someone who could give you some information on what they look for when they recruit. Do they look at work ethic and a desire to improve? Is it more then just stats. Ask if they would email you the info and then show your daughter the email. Then it isn't a matter of a conflict between you and her. It is what it is not from your mouth but the college recruiter's. Ask her if this is really what she wants. Tell her you need to know because if it isn't you need to start thinking now of other ways she is going to get into college and what kinds of financial aid she will need and so on.