This depends on what the alternative is. Your loan of .99% is very favorable rate. If you have the 15,000 right now but only hold it in your checking account or cash then you might as well just pay it all off(assuming you have an adequate emergency fund).
If you have an investment vehicle you feel can successfully yield more then .99% then you might want to consider investing that money instead, while paying the minimum on your car loan.
Also be sure to check the .99% is not an introductory rate which increases later on.
It comes down to weather you can get a better return then .99% investing that money or weather you rather just pay off the debt and not worry about it. If you don't want to bother investing the money, than just pay it off...
I also assumed you have no other revolving debt with a higher APR. If you do, pay off the higher APR debt, first.