I'm 15. My nipples are inverted. One of them comes out rarely & other one doesn't look like its ever formed. Any suggestion?

There are three basic degrees of severity of inverted nipples. The treatment is a bit different for each of the types. It sounds like you have the most severe type. I think that endoscopic release of the fibous tissue and dermal grafting gives the best result wile trying to preserve your ability to breast feed. This requires that the ducts are protected during the surgery. There are many techniques that simply cut them so it depends on your concerns. 

A small surgery can fix your problem.  Please see a board certified plastic surgeon for a consultation.