I'm looking for a set of snow tires and found someone selling a set of snow tires on 15 in. steelies. Would 195/60/15 fit on the MCS?

 

You should be okay with that size, Henry, although 185/65/15s (which I run for winter) will be a little "truer" to the 195/55/16s that were one of the two stock wheel/tire sizes available on the '05 MCS (and presumably on the '04s as well); 195/65/15s would be somewhere in the middle:

Check this out; it's fun: http://www.1010tires.com/tiresizecalculator.asp

 

Speedos show a slightly higher speed with smaller tires. Obviously taller tires are better in the snow. Also smaller tires lower the car very slightly but otherwise should work