126 Wheel swap
 

Would 15 inch wheels from an 86 190E fit on a 85 380SE without any modifications?

The 126's wheel's offset (ET) is going to probably push the wheel face farther out than on the W201's rim. Do you know the width and ET of the wheel you're interested in? If so, there are online offset calculators that will do the calculations on the differences. The wheels themselves will bolt up.

They fit and your car will roll, but they will make your 126 look like one of those pickup trucks that is able to run on railroad tracks with the inset wheels to fit between the tracks. They sit in too far and give it an odd look IMHO.