How do I convince my mom to let me pierce my nose?

I'm 15 and a half and a good girl. I get good grades and all that. My whole life I've wanted to get my nose pierced, just a really small stud, the ones that look like a sparkly freckle. I asked my mom and she says no. She even agrees with me that they look good, and says she consitered getting one herself in her youth. Two of my aunts had them and took them out after college and there is no hole visible. I have freckles anyway so it wouldn't be noticeable. I ask ehr why and she says when I'm 18 I can do whatever. But I'd just love one now. I realise I'd take it out after college, I'll hardly wear it when I'm 40, and I'm prepared to have a small mark if it ends up that. How can I convince her?