A lot of this does sound normal for a teenager, angst about friends, school, comparing yourself to others, and to your own ideal. Give yourself time to adjust. Focus on the work at school, and consider getting involved in some school activities/clubs (sports/theater/other) where you can be doing something with others around a shared interest. At 15 so many things are changing inside, you are just "becoming" in a sense.
I remember my son expressing surprise, a few years after high school at how unimportant the things he thought so important then actually turned out to be....things he worried about.((((((((hug))))))))))