Rumors of all F-15s retiring are unrealistic. We're not buying enough replacement F-22s for the F-15Cs, and there isn't a replacement for the F-15E anywhere in the procurement planning. The F-15E may be our last real strike fighter, ever. Neither the F-22 or JSF can come close to the range, endurance, payload, and dual-crew flexibility of the F-15E. They'll keep them flying as long as possible.
Boeing is building up an F-15E variant with a dramatically reduced radar cross section, and that might end up being our next strike fighter. If they can manage the RCS well enough, it might get past the pentagon mandate to buy no "non-stealth" combat aerial vehicles and be a very affordable and capable alternative to more F-22s or a strike variant of the F-22. It's a long-shot though, and it might merely end up as an export variant for countries that share my low opinion of the JSF but can't buy the F-22.
As for the F-15Cs, they'll keep flying them until the wings literally fall off because we can't meet even our peacetime defense requirements with the F-22, let alone go abroad and do anything requiring air superiority. The JSF is supposedly going to replace the last couple hundred F-15Cs, but that'll go over about as well as replacing the F-15C with the F-16 did. The JSF is nothing but a fwd-aspect-stealthy viper with better radar/avionics, not an air supremacy fighter. Hell, it can only carry a couple AMRAAMS... what a piece of crap IMHO.
But it's "joint", and in our current socio-political-military environment that means much more than actual capability. That's why I'm flying the T-6 built to US Navy specs (and that they later demanded get upgraded after USAF bought the first several hundred) instead of a real T-37 replacement built to USAF spec.