Am I a normal size for a 15 (almost 16) year old girl?

Yes because I am 15 going to be 16 in 5 months im 5'2 122 pounds and i have a 36c or d depending on the bra(:

It's somewhat different for different people. For me, I'm 5'1 and 120 pounds feels like a very comfortable weight and looks good on me. lol Heck, at 150 pounds I feel a bit overweight, but no one thinks I look overweight. It depends a lot on how you're built, but that sounds a bit underweight. No need to worry about your bra size; whatever size cup you are is fine and healthy.

sounds super normal. I'm 21 and I wish I had those measurements lol

Yes, perfectly normal. You are still growing.