Thanks for the brick wall of skepticism. I found the picture browsing another forum http://www.alien-ufos.com/forum/showthread.php?t=13419 but thought this a better place to start my research is here where people are generally more informed and level headed.
The idea of putting forward swept wings on the F-15 seems quite obvious because after the X-29 that’s what we expected the next fighter to have.
The picture may be fake or it could just be so poor quality because it’s been zoomed up. I’d rather reserve judgment until more information on the YF-24 can be dug up.
My research suggests that a manned YF-24 definitely exists and I think the F-15 story is at least as plausible, no more plausible, than the YF-23 bomber story.