Welcome to the club! It took 9 mths or so to put that weight on, so it's definitely not going to fall off in 6 or 7 weeks. Yes, there are the "blessed few" who walk out of the hospital in their pre-baby jeans, but truly, you are blessed to only need to lose an additional 15 lbs. And those are & always will be the most difficult lbs to shed.
I was told over & over how those 15 lbs would "fall off" once I stopped nursing, or once my little guy started crawling, or once he started walking (since I would surely be getting enough exercise "chasing" after him). So I waited. And I eventually stopped nursing. And I chased. And the weight was still there, 2 years after I gave birth.
That's when I got tired of seeing pics of myself still looking thick in the middle, the arms & the face, as though I had recently given birth...UGH. I took the plunge & joined a gym. Nothing much happened until I got on a treadmill several times a week & got my heartrate up to 160 for a good 30 minutes. 4 months later, I weighed less than when I got married, which I truly believed was never even possible again!! I was so mad at myself that I hadn't taken action earlier.
So, I've now got a 4-mth old & yep, those 15 lbs are back - and I only gained a total of 20 lbs during the pregnancy. Only this time I'm taking action much earlier, knowing that a healthy diet & regular exercise are the key to being fit & trim - at least for me. I would assume some form of exercise is going to be the way for you as well. I also have seen great sucess from friends who have joined Weight Watchers, even for those last 15 to 20 lbs.
My suggestion: take action NOW, regardless of how long you plan to nurse or when your little one starts to crawl. It just gets more difficult to establish a routine the older the child gets, so start something now & see what happens!
Good luck!