Is it bad for a 15 year old virgin to use tampons?

No, it's not bad for a 15 year old virgin to use tampons.

A virgin is someone who has not had sex (however the individual defies sex), that's it - there is no difference between someone who is a virgin and someone who is not, the vagina is not changed by having sex so no reason why a persons sexual experience would impact on whether or not they can use tampons. Although tampons aren't recommended to teens, due to higher risk of TSS as a result of more delicate vaginal tissues pre-puberty or in early puberty and lower chance of having TSST-1 antibodies, as long as you understand the risks and follow precautions to reduce your risks it is okay.