The factory size is: 225/60-16
Listed on the driver's door post.Original Equipment Size: 225/60-16
Base models: P225/60R16; Impala SS: P235/55R17.....
It will run well on 215/70x 15.
What size engine.
Have the wheel bearings checked, as well as the alignment.
Look on the drivers side door at the specs decal.
24
P225/60R16
Either a 3.4 or 3.8 V6
6.5 in the front. 6X9 in the rear.
On a 2000 Ford Windstar : Open the drivers door , and on the latch pillar will be an information sticker that shows the original size of tires on the vehicle from the factory
I suggest you go to www.tirerack.com You will find the correct answer there.