In multiplayer matches very often the first hint of an F-15 is a missile coming at you, and they don't miss very often. If you know they are there, chances are that you won't see them because of distance or altitude. The only thing you can do is try to find cover but if they're high enough they can just look down at you anyhow. Another thing you can try is point your nose their direction and fire an aim-9. Sometimes they see it and evade as a precaution, giving you time to try to hide.
Just one more note. Turn your jammer off. It's like a beacon for the F-15's and it simply leads them to you.