I wasn't going to respond to this post, because it is like SO many others that have been posted here - two kids wanting to date but the older one is concerned about the legalities of dating the younger one - and your responses are as always, too.
Yes, if these kids have sex, the 18 year old boy can be in BIG trouble with the law. And the 15 year old girl can be in BIG trouble if she picks up HPV or some other disease or gets pregnant. And if they drink or do drugs, they can BOTH be in big trouble. But, for heaven's sake, they can LEGALLY DATE. They can go to movies, they can go to proms, they can go to the beach, they can hang out at each other's houses, they can walk to classes together. And, whoa, they can even LEGALLY KISS each other.
Three years is NOT that big of a difference. High school seniors date high school sophomores all the time. High school juniors date high school freshmen all the time. And some high school sophomores date middle school seniors. Not every 18 year old boy is looking to date a younger girl for sex - sometimes 18 year old boys relate better to the younger (but mentally more mature) girls. Sometimes 18 year old boys feel better dating a younger girl, who may look up to him, rather than dating someone his own age who may think he's a dork. High school classes are often filled with kids of different ages, and sometimes kids just "click" - and they don't even notice the age difference until someone points it out to them and scares them into thinking there must be something wrong with them if they like each other.
I have worked with a LOT of high schoolers. I know a lot of college kids. And their dating does not concern me NEARLY as much as those kids who NEVER date or, for that matter, it doesn't concern me nearly as much as an old geezer trying to turn back time by dating a 25 year old. These are the ones that are far more worrisome and, in my opinion, troubled.