In general, you're almost certainly no longer on the path to calculating anything that should be called TCO once you've started removing costs associated with using the item. Apart from that, you're probably not on your way to a very meaningful cost comparison either.
Registration: $600/year
Insurance: $1,500/year
Gas: ~$2,700/year (15,000 miles @ 30mpg @ $5.50/gal)
Loan: ~$3,500/year if I had borrowed the entire price of the car on a 60 month loan and then kept the car for 15 years as the GP stated
Maintenance: Certainly less than $1,000/year, much less in most years.
And in some states registration and insurance could literally be a third of what I pay. Gas could easily be half. I can't imagine anyone is paying $12,000/year for any non-luxury vehicle.