Aside from the original flipping of games immediately after the release of the repros in 2007, the actual number to sell since is extremely low. The standard of the game and the difficulty in replacing it down the track is a major hurdle to overcome if you decide to sell. At $15,000.00 I can't say I am not tempted - I've had the game a fair while, know it well, and someone else would I imagine appreciate it more than me by now. But I still love playing it, and can't imagine selling unless there was family/financial reasons to thin the heard. I guess many others with one would have the same sort of situation, so supply stays very low.
Is it worth more than an MM for example? I think so (I like it more) - those seem to be $10-$12K for a restored example, and as the repro BBBs are only a few years old and pretty much only HUO, I guess that gives a perspective to the $15K sort of price.
Fun to speculate, we'll need to see a few local sales to really get an idea, but I doubt that will happen.