Halo: Reach - First 15 milion seller ?

[Steroid]

I highly doubt it.

There was a 3 year gap between Halo 2 and 3 allowing a lot of hype to build. That kind of hype build up won't be there for reach 1 year after OSDT and will be competing with significantly more FPS's then Halo 3 ever had to contend with.