Where did you hear that 15 pounds was normal? Have you read the book, it has some stats there.
For women:
Less that 20 pounds to lose anywhere from 2 to 6 (averages)
20 - 50 pounds to lose anywhere from 3 to 9 (averages)
Over 50 pounds to lose anywhere from 4 to 12 (averages).

From the sounds of it, you have a good metabolic resistance since you are not on the low end of the spectrum.
Also, we can't compare ourselves to others - which is something I try and keep remembering. We also don't lose like we used to I'm finding. I've never been this heavy - even after kids (of course the anti depression meds had a lot to do with this last round of weight) - and I've never had such a hard time getting it off!

Good luck tho and keep plugging away. I figure I better prepare myself to be the tortoise and not the hare! LOL
Traci
Oh, and 6 pounds is great!!!