Your thread from just two weeks ago said "How to increase arm strength? I have stuck on the same weight since long.."
So are you seeing progress or not? Real progress like measurably more muscle, more visible definition, and/or using more weight for more reps.
Is that 15 sets total (like 9 sets of biceps and 6 sets for triceps) or 15 sets for bis and 15 sets for tris? If you're doing it twice a week, I hope it's total.
Your profile says you're 5'10", 98kg/216 pounds, and 15 years old. I'm going to go out on a limb and say, no, you don't "need" to be doing 15 sets twice a week, but it depends (a bit) on your goals, nutrition, and especially what your other training looks like throughout the week.
Can you list the days, exercises, sets, and reps you do for the week (for everything, not just arms)?