As a minor it is your mothers choice, when you turn 18 it will be your choice.
I am lucky to have my mother trust my decisions. I ride with a helmet on green horses and horses I do not trust. HOWEVER, I also have the abilities of a spider monkey....I can cling to a horse who is bucking, bolting, crowhopping, etc no matter what. I've been like that since I was little....No way in hell are you going to get me out of the saddle unless you are extremely determined or I choose to step off. Is it impossible? Hell no. However, I will not wear a helmet when I am showing any sort of western discipline. For that I either wear a cowboy hat that matches my show shirt or no hat at all, depending on the level of show. I will where one when I am english (Except dressage, I wear a hat in that, and I rarely show english anyhow) because it is required and/or the norm.
Long story short:
If wearing a helmet a safe choice? Absolutely.
Can you do anything about your helmet situation? No.
Later in life will you be able to not wear one? Yes.
When you grow up it will be your choice. Until then, tough it out :)
Oh, and I HATE troxels. Hatehatehate. I cannot even express how badly I want to throw every single one of those ****ed things into the fiery pits of hell.
Tipperary is the only way to go in helmets, IMO