Which affordable current brand/model 15 inch tire sizes will fit my 240 sedan?

I have always used 14" tires on my (original) 14" wheels. However, I am considering putting on 15" wheels/tires because 14" tires are 1) harder to find 2) fewer choices 3) more expensive than 15" tires.

I spoke with my mechanic and he was not absolutely sure 15" tires will fit the rear. I do plan to buy old steel 15" rims from him.

And of course tire places are no help at all- their "books" tell them only 14" tires will fit.

My '91 240 Sedan has over 350K miles on it, so the suspension isn't in great condition (might sag a bit).

I really don't know anything about tires. So I was hoping some of you would recommend specific all season tires sizes that I could buy to fit 15" trims and would cause no problem fitting and driving my car (a daily driver, city/highway only).

Searching the Brickboard archive I found some old discussions that suggest these would be good to use: 205/75R15, 205/60R15, and 195/60R15, but not sure.

Thanks!
Keith Ostertag
New Albany, IN