How do you convince parents to get cartilage pierced?

You can't. A parent's job is to raise a good kid and to stop them from doing things that may negatively affect the kid's life. I'm assuming that the 15yo is asking the question, so I'm sure that you don't think anything is wrong with it, but your mom may view it as something only "bad" kids or druggies do (for example) and doesn't want anyone thinking her child is either one of those. Do what the rest of us did, wait until you are 18, then you can do anything you want. You may look back and realize some of your parent's decisions were for your own good, or not, as the case may be. Not necessarily in your case, but when I look back at the things I wanted to do...geez, thank God I didn't get a chance before my parents stopped me. As I always tell my brother: BE GOOD! Has anyone informed you that a nose piercing could cost you your life? Even a slight infection in your nose will go straight to your brain and kill you. Is a nose ring that you will hardly ever see worth it? Have you tried sitting down with you mother and asked her her view on the piercing? Ask her to sit down and listen to your reasons that you want this piercing so bad that you don't want to wait 3 more years. And also let her explain why she don't want her daughter getting it done right now. Do this without any confrontation and show her that you are mature maybe that will change her mind. Good luck, be safe!