Don’t forget that the F-15 (and A-10, which is still a workhorse) is older than Star Wars, the F/A-18 is older than Empire, and the F-22 is as old as the Special Editions. Plus, all of these planes serve different purposes for different branches of the military.
As I said, Soviet Union effectively collapsed in 80s.
The same is true for Star Wars: The TIE Interceptor serves as a specialized air-to-air fighter while the the normal TIE Tighter is more of a multi-role craft from all the canon I’ve ever known. Same as the TIE Bomber is a specialized bomber, or the TIE Striker is a specialized atmospheric fighter/transport.
Seeing how OT space combat is based on WW2, there are basically three main carrier-based roles: fighter, dive bomber and torpedo bomber (I guess the two are the same in OT). TIE fighter obviously filled the fighter role until it was obviously replaced by TIE interceptor. Of course, like in WW2 the replacement cannot happen immediately so we can still see some TIE fighters at that point. But the fact is that in ROTJ battle the two do exactly the same role.
No major military just has “one” model of fighter that they replace continually. In World War II there was the P-51, the P-40, the F4, F6, and F8, P-47, the F4U… and that’s just some of the American planes I can think of off the top of my head, several of these went on to fight in Korea as well and some saw active service until the late 60s and early 70s.
When it comes to WW2, there were specified roles that were continually replaced by newer models. Primary US land-based fighter: P-40 replaced P-36 and P-51 replaced P-40. Primary US carrier-borne fighter: F4F replaced F2A and F6F replaced F4F. And so on…