Hi, sorry you're going through this, I also have a difficult relationship with my mom. Not all parents are like her, and I'm sure when/if you become a parent you'll love your children selflessly. You must also remember that our parents grew up in a different era than us, and our ideas of what a parent should be might not match up with what they think a parent should be.
A lot of this might also have to do with your culture, is it a strict culture? A lot of times, parents will want their child to achieve more financial success than they did so they will push the child (quite ruthlessly) to achieve higher grades. Higher grades don't automatically mean financial success, but it sounds like your mom believes it does. It sounds like you're already a great student and you're very smart.

So if I were you, I would just try to lower my anxiety. Don't think about your anxiety too much, all you need to do is focus on your school and just do your best. You're 15, and that's automatically a hard age because you're starting to go from being a child to being an adult. Sounds like she's giving you tough love, and she thinks that will make you preform better, but it sounds like it's doing the opposite. So just don't argue with her anymore, let her say whatever she wants, and just focus on your studies.

When you're old enough, you can move out and make a life for yourself, independently.