I've moved your topic over to the Game Help board, as I believe this would be a more appropriate section for your issue.
Please keep in mind that bans should not be discussed on the forum, and if you are seeking trouble with a ban, you are encouraged to contact staff. The 15 minute ban happens when you log into the account incorrectly at least five times, so it may not be someone trying to logging into your account. Make sure you are entering in capital letters correctly and ensure that you are not using the numpad (numbers on the side of your keyboard) if you have any in your username or password. Make sure you've activated the account. Feel free to contact me if you're still experiencing the problem. c: