Here's what is probably the best natural way to lose 15 lbs in 2 weeks (or at least look like you've lost it):
1. Do a 2- or 3-day raw diet
For 2 or 3 days consume nothing but water and raw fruits, vegetables, nuts, and seeds. That's a simple version of a "raw diet" and it can help you reach your goals more quickly. Eat and drink as much as you want and as often as you want. Buy organic version if you can. This is a healthy, natural way to cleanse your body, boost your energy, and lose a couple pounds quickly.
2. Start doing interval-based workouts
5 days a week, do a short, intense workout based around high-intensity interval training. Do both full-body strength/resistance workouts and strict "cardio" exercise in order to get the maximum amount of fat loss benefits. Keep your workouts to under 30 minutes and keep the intensity high. Get the help/guidance of an expert if possible... especially if you're new to exercise!
3. Start eating a strict "paleo" diet
For the next 2 weeks, eat nothing but paleo foods: those foods humans evolved eating over hundreds of thousands of years. Examples: meat, eggs, fish, nuts, seeds, fruits, and vegetables. Avoid all grain foods and most starches, especially white potatoes. Try to eat a small protein-rich meal or snack every 3 hours during the day. Drink LOTS of water and unsweetened teas. You'll begin to lose pounds quickly and you won't have to worry too much about calories, since these whole, natural, unprocessed foods are made up of only "good" calories that your body thrives on.
That's it: a simple and healthy way to pounds and body fat quickly. This is definitely one of the best ways to lose 15 lbs in 2 weeks. At the very least, the strict "natural" diet and effective full-body exercise will make you look and feel a lot better in a very short amount of time. So get to it and start burning off that fat right away!