If you don't want to wear diapers, you could try to contact a professional, limit your consumption of liquids or food that is high in liquids like fruits. As you are 15, I don't really think this could help, but if you cannot/don't want to use any of the methods, I think you may have to do it wherever you can (bush, patch of grass, near a fence) etc. This is a stupid suggestion, try not to use it.