I don't know if going from a 15 year old car to a 10 year old car would make much difference. When you're dealing with vehicles of that age, how they were maintained is really more important than whose badge is on the engine shroud, or the car's age. And cars nowadays are just so danged complicated that whenever anything breaks, it ain't gonna be cheap.
In fact, if you choose wisely, you might be better off going from a 15 year old car to a 20 year old car! Especially if you picked something simple and RWD, like a Caprice, Crown Vic, Gran Fury, Diplomat, Cutlass Supreme, etc. They'll probably nickel and dime you more than a 15 or 10 year old car, and if they're carbureted they might be more cranky on a cold start, but you'll probably avoid some of the really expensive repairs, simply because there's nothing really expensive to repair!
Most of my driving these days is split up among three vehicles: a 2000 Intrepid with 116,000 miles, a 1985 Silverado with around 117,000 miles, and a 1979 New Yorker with around 90,000 miles. I actually trust the Intrepid, because I bought it new and I know how it's been maintained. The two biggest things this particular model of Intrepid is infamous for is transmission failure and engine sludge. I always get the tranny serviced at 30K mile intervals though, and I've never had any problems. Plus, it was usually the bigger engines like the 3.2, 3.3, 3.5, and 3.8 and higher GVWR vehicles like minivans that usually saw the most failures. I don't think the 2.7 in my car has enough torque to strain the tranny that much. As for sludge, my mechanic told me that if you let the oil changes go 7-10,000 miles, then yeah, it'll sludge. I usually do mine at 3K intervals though, very rarely stretching to 4-5.
Now if I were looking for a used car, I think I'd be a bit leery of a 2000 Intrepid, unless it had service records and I could see it had been lovingly maintained. Otherwise, I think I'd rather take my chances with a left-over police car from "The Blues Brothers"!