I know it's been said already, but for anyone who missed it..
The current workaround to make the mod work, is to get in the FC version of the F-15 first, then back out. Doing that seems to "load" the need file to your session and the F-22 mod should work for that instance of DCS.
If you close the game, you need to repeat the steps to "unlock" the F-22 mod again.