You have to remember weightloss depends on the amount you weigh, genetics, metabalisom, etc. In my opinion, the bigger you are the more you will lose.
If you're fasting for 15 days and want to lose 30 pounds that's 2 pounds a day. I guess it's possible, but 12-20 pounds seems more realistic. I lost 25 pounds on a 2 week juice and water fast, but I'm heavier then you. I also didn't exercise that much so I could have probably lost more.
Anyways, keep us all updated how it goes and Good luck. I could easily be wrong. Heh. =)