A $15,000 car loan could cost you anywhere from $1,000 to over $5,000 over time, depending on the APR that your lender offers you. Your APR will be largely determined based on your credit score. If you have an excellent credit score, your APR will be much lower than it would be for someone with a low credit score.
If you want a more exact figure, shop around with some lenders to learn more about your interest rate options. Once you’ve gotten quotes from a few different places, you’ll have a better idea of how much a $15,000 car loan will cost for you specifically.