First of all, 15-year-olds do not get bottom surgery. This is just scare-mongering by MAGA extremists.
Secondly, yes: Gender-affirming surgery is settled science and is approved by all competent medical associations.
You want to know who gets a lot of gender-affirming surgery? In the United States, cisgender men with a condition called gynecomastia develop breasts due to a hormone imbalance. This is a completely benign and harmless condition and yet every year, over 24,000 men have them removed. Nobody says "why are these guys mutilating their bodies and removing perfectly healthy tissue!!!" even though they are doing it precisely because they are experiencing gender dysphoria.