It takes 21 days to form a habit. Thus, practice meditating for 15 minutes for 21 successive days, and you are sure going to reap the benefits of doing so.
Meditation is not about turning off your thoughts. Rather, it is about getting in tune with them. It is extremely difficult at first because aside from the other thoughts running around, people might start thinking to themselves, “stop thinking” and lose focus altogether.
Don’t think too much about the results. Just do it. Read more about it here: For a more centered life, meditation only requires 15 minutes