Yes it is illegal in every sense of the word for an 18 year old to touch a 15 year old in any way.If there is no penetration but heavy petting its called child molestation and he could very well go to jail.Just because hes not having sex with you,he is still touching up a minor until your 18 also.And intercourse isn't necessarily just penetration,it is the whole act of making love to someone.