Will not go over 15 MPH

Hello, I'm Danny.

That means a code is stored in your vehicles computer and therefore the computer has put your car into "limp mode".After the problem is fixed and the code is cleared you car will go back to normal.If you don't have access to a scanner/code reader most auto parts stores have a tool loaner program and can loan you one. Autozone will check your codes for free.Here is a tutorial for you to read about how to check codes:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

After having the code(s) read get back to us with the code information and we can properly diagnose this condition.Hope this helps and thanks for using 2CarPros.