Leather seats take a beating from the sun, jeans, and spilled coffee until the cabin starts to look tired and feel stiff. Keeping a car nice isn't cheap between routine maintenance, fuel, and upkeep, but you can save a bit by booking during the slow winter months when detailers are hungry for work and prices soften up.
We can use a financing window to spread out the hit, but remember that financing is just for smoothing cash flow, not a discount. You still want to negotiate the service price down on its own merit before we talk about how you are going to pay for it.
That 0% intro APR for 15 months on purchases and balance transfers is a deadline, not free money. If you still have a balance left when those 15 months run out, standard interest kicks in on the whole original amount.