15 is totally fine for make up.
I started wearing it about age 12- and that was the age of punk rockand Joan Jett with the heavy black all the way around the eye liner- didn't have much of my own but went to school and in the locker room we all put our stuff together and had more than enough, lol!
Ohhh the hygiene, ha ha!!
My daughter started wearing it about 13-14, I think. Nothing big, just mascara and gloss. She's 22 now and she still wears about the same- mascara, lip gloss.