First, you're at a tough age. I remember being 15 (I'm 57). At that age, I had doubts. I realize now, that is normal. When I went to my 10 year reunion a lot of years ago, I found out that just about everyone felt the same way I did. So first... Some of what you are feeling is normal just because you are a teenager.
You have the same worth as any other human being. They are no different from you and you are no different than them. You need to value yourself more.
I had bypass surgery three years ago. It's at a moment like that you understand how lucky your are just to be alive. I would suggest to you that you will find yourself, you'll find what you enjoy doing, you'll make some friends along the way. All that will make it "worth it."
I hope this helps some.
All the best.