I think you are doing great.

Because you are 15, somuch depends on your own body's schedule for growth spurts. Give yourself time to grow up, you're doing great.

I would not suggest really heavy lifting unless supervised by a coach or knowledgable adult who is looking out for your best interest, not just a buddy standing there spotting so you don't drop the bar on your neck.

If you want to gain muscles start including weight lifting in your program. Be sure to do multi-joint lifts, such as squats, dead lifts, benching, pull ups, chin ups and dips. Try not to concentrate much on the single-joint lifts (i.e.), bicep curls, triceps push downs. When lifting do lifts that work body movements that are functional or sport related. Example would be doing squats to help increase jumping for any type of sport that involves explosive jumping.

To gain weight you have to eat more calories than you burn. When adding calories, try to stay away from adding too much fat. While you can get fat from eating carbohydrates or protein, your body likes to use carbohydrates as fuel more than fat. To gain muscle, in addition to eating more you have to stimulate your muscles enough through resistance training that while they recover, they'll get bigger and stronger. To get an efficient workout you might want to join a gym if you aren't already a member.

Guide to Gaining Weight -

well i do almost exactly the same as you and people say that i exercise too much but i have been doing it for awhile so i have plenty of muscle, i think that is a good calorie count as long as you stay active! and yes you are gaining muscle the right way!

I would suggest you double your caloric intake if you are trying to build muscle. 2500 calories is probably just enough to keep you going.