Hearing that metallic scrape every time you pull up to a stoplight is a quick way to ruin your week. Keeping a car on the road means dealing with routine wear and tear like pads and rotors, and the bills rarely come at a convenient time. When your car needs new stopping power, you want to get it handled safely without draining your entire checking account.
Timing matters more than most people think. Auto repair shops are usually dead in the late winter after the holiday spending slump, meaning mechanics are far more willing to cut you a deal on labor or bundle the parts. Call around during these slower months to get quotes before you commit to a shop, and negotiate the price of the job on its own merits before you ever mention how you plan to pay.
Remember that the intro window is a strict deadline, not free money. If you still carry a balance when the 15 months are up, interest will kick in on the remaining amount, which defeats the whole point of spreading out the payments.