If i'm understanding you correctly, you want to lose 15lbs in a month? if so, yes thats doable and very reasonable. you can lose 15 lbs with diet and exercise. But since you are wanting to fast, obviously depending on your body, on average most lose .5-1lb a day. I fasted for 35 days, and lost 41lbs. (i averaged 1.17 lbs a day)hope that helps.