Alright buddy, let's get this sorted out. There's something wrong somewhere (which is good news!), that's not the performance you should be getting.
First of all, show us your settings (screenshot the options page). 22 fps sounds low but flat shadows = off and a few other settings can really take a toll.
Second, attach a mission in which you get poor performance at the beginning. "Create fast mission" randomizes a mission so we can't use that for testing.
Also, that "video memory" number that the game is reporting is always that high. I'm not sure how it works but it might be VRAM+RAM occupied by the game, in which case 6 gigs is fine.