I'm at 14 big blind / 100, playing 3-4 tables at NL100 (full tables) after 25k hands.

And I'm by no means a special poker player. I know my odds, I play tight, I'm aggresive on the flop, rarely bluff and let the fishes pay my big hands . So I think that a very good player can easily win 20-30 big blind.

At 14 big blind, I appear to be one of the best NL100 player at the site I play (UB). I just looked at the other regular players stats in PokerTracker and noticed that half of them were breaking even, and the other half were between 2-13 big blind.

Conclusion: For a regular player that will study the game but that has no special poker skill, 15 big blind is definetaly possible.