well, not that similiar but, almost the same ceiling, speed, size(well, the F-18 is a little bit more smaller.)
Both have 7 external hardpoint.
http://www.aerospaceweb.org/aircraft/fighter/f15/
http://www.aerospaceweb.org/aircraft/fighter/f18/
Both have 3 mfcd (probably the same function) they are aircraft, so they are doing the same thing fly, fight and drop bombs.