Just curious...
They added armor to it and re-positioned it as an MRF (Multi-Role Fighter). It now is supposed to bombing, CAP and other ground-related activities. Although an F-15 certainly CAN do that, its design is for air superiority. That is no longer true for the F-22 (Lightning or Raptor).
They were doing tests (I can't recall the source) and the F-22 was usually defeated in air combat tests against the F-15.