I think most of what you see out there as far as military AI are FS2002 models that are used as AI.  For the F-15s you're looking for I know you can find some here in the FS2002 military downloads section.  The military AI I've seen are these 2002 aircraft just being used for AI.  They do cause a performance drop in my system which is middle of the road by computer standards so don't expect too much if you go with these FS2002 models for some military AI.  

Otherwise there's not much to choose from if you want stuff that looks half-way decent.