I'm still relatively new to DCS (about 40 hours or so) and currently only have the FC3 module. I've been flying the campaigns that come with FC3 to learn the planes and the basics before getting a full Fidelity module.
I have a few issues with the f-15 that I've not noticed in the Russian planes. While it excels at BVR it feels pretty much useless at all other times. It bleeds energy way too quickly, even during shallow turns and once an su-27 in on your tail it's very difficult to lose them or turn the tide, doing a tight turn and dropping speed makes it far less maneuverable, therefore harder to get away. I know i'm not supposed to get into these situations, but like i said, i'm still learning.
What's the best way to keeping distance between you and the enemy while still being able to fire off missiles, having enough time to react to missiles being fired at you and not allowing your self to get into situations that will end up with you being painted on the side of a mountain?