Is 140, 13 yrs. old, and 5'6 fat?

Whoa, there. 140lbs on someone 5'6" is PERFECTLY healthy. You're not fat at all. Just eat healthy and exercise (sounds like you already do, being on the basketball team...don't worry about going to the gym). You don't need to lose 15 pounds...that actually would put you in the underweight category. If you think you're fat and you can't stop thinking about it, please talk to your mom or another adult. You don't want to develop an eating disorder. It can kill you.