Mercedes did produce 15" alloys and a steel wheel for the W210 so I see no reason why a W124 wheel wouldn't fit. It will be 7mm closer to the caliper than one designed for a W210.
Worst case scenario would require 5-10mm hubcentric spacers found on eBay.
Edit, W210 15" alloys are 7J , so a slightly narrower wheel (6.5J)should be OK to clear the caliper.