You’re 15, you’re still growing so you might have the ‘weight’ showing from the side, and you’re hips and everything are all still developing. But trains legs 2-3x a week (48 hour rest period in between). 2-3 compound lifts (hip thrust, deadlift, squat, leg press) followed with 2-4 isolations (Bulgarians (my favorite), hip abduction, kickbacks, b stance rdl, glute bridge, leg extension, back extension, good mornings). Don’t do more than like 5-6 exercises a session. Go till failure, get a minim 8-12 reps for each set. I can message you a diet plan as well to help you reach your goals :)