It is a real bomb, Air Force has been working to get better bunker busters for a few years now. Not sure how well it works, not a scientist. But the newer ones being worked on now, are half the size of this bomb, and will be rocket powered. Should have enough kinetic energy then!
I would wonder about the power of the shockwave from this 15 ton bomb, the warhead is 2.4 tons.
http://en.wikipedia.org/wiki/Massive...nce_Penetrator