I wouldn't say that it's possible to lose so much of weight in such a short span of time.
Also there are no medicines that can make such a thing possible.
Even if anyone suggests you or gives you something, you should avoid as they can cause some serious side effects.
There is a safe way of losing weight naturally, I always encourage all my patients to take up such a method rather than "quick and easy" ones.
Think of it this way, the weight has been gained gradually therefore it will take time to make it go.
Here are a few tips to reduce weight.
1. Drink lots of water.
2. High protein, low carbohydrate diet must be followed.
3. Intake of calories should be less than the daily requirement, and you should get most of the calories from fruits and vegetables.
4. Avoid rice and rice products. Green tea twice a day.
5. Burn more calories than you have taken. Cardio workout must be followed. Any form of excercise which keeps your heart rate raised to a level of 140-150 burns fat effectively.
6. If you are very dedicated and follow all these sincerely you would be able to lose 15kgs in 4 months.
All the best.