How can i convince my parents into letting me play m for mature?

Okay im 15 years old!!! I have a 15 year old twin brother. Our mom is the one who wont let us play m. Our dad hasnt said anything. My brother and i fight and bicker alot. <--extra info just incase. So how can i convince her to let us play M??? Btw she is stubborn, kinda redneck, wont change her mind, naggs and talks alot, and vain about looks, and she smokes. So how guys??? How???