Do what you enjoy. I done some subjects at A Level which I did not enjoy and it reflected in the results, compared to those I did.
You're 15, get the secondary education, Maths, Sciences and English done with good passes and that will always benefit you.
If you enjoy Maths and Physics, and do well at the secondary level, then they're always useful
(from a mentored/sponsored point of view any ways). I doubt the ground school ventures into the realms of partial differentiation though.
Good luck.