15 pounds in a month

So I'm almost 15 And i weight 245 and I'm 5'6. And im doing weightlifting next month and I want to lose 10-15 pounds by or around October 17. I already try to drink a gallon of water a day. I don't eat that many sweets. And really only eat 2 meals a day plus a snack or 2. Plus on a daily basis I get about 2 miles overall from just daily activities ( walking to and from school. Class to class and running in gym). What are easy and fast ways to lose this weight? P.s. the weight loss isn't necessary but after I saw what I weighed (I really don't even look it) I decided that I want to start losing weight for my own self