You know, no matter what reason you have for doing the Master Cleanse, if you do it correctly you are going to both lose weight and cleanse your body. The downside of using any fasting program for weight loss is that much of the lost weight will not be from body fat but from water loss and the results of an empty digestive system, this weight is always regained very quickly. In many people weight loss also occurs because of muscle wasting, but the Master-Cleanse should contain enough carbohydrates to keep this to a minimum. Another downside to any ultra low calorie diet is that the metabolic rate will slow down and the rate of weight loss slows and weight may be gained back at an even faster rate. A fifteen pound weight loss in a month's time is not an unreasonable goal. You could probably lose it by doing the Master Cleanse. You might also want to try a raw foods diet similar to the Fuhrman "Eat To Live" plan where you can easily lose up to 20 pounds in six weeks. A combination of high fiber raw foods and a couple of weeks of The Master Cleanse should help you meet your goal.