I really don't want to be mean but I just watched your video F-15 vs PAK-FA and I think you're not experienced enough in combat. 2nd, AI is always pushing aircraft to it's limits, like 101% of it's performance, when player is not able to do that, it's just impossible. I'm flying on F-15 for a really long time, I can easily beat an Su-27 (depends on opponent's skill level) but still, I like challenges ;). F-15 is like a brick, if you want it to fly you gotta throw it really hard, it doesn't like to go slow, and 15-20 miles of detection range is still enough to effectively engage target.
P.S. You have taken shot without authorization ;).