It's impossible to increase your height in such a short amount of time. Your genetics play a big part in what your overall and final height will be. If your parents and other relatives are short, generally you will too. If you have a mixture of tall and short people in your family, then you won't have any idea until your reach your final maturity between the ages of 18 to your early 20's. You can have periods of growth spurts but it's not in that short of a time period, such as 15 days.