There are definitely fakes of the 3515.20.00 out there, but all the ones I looked at differ in a couple ways on the back. This link is to the only one I could find that appeared legitimate (terribly overexposed pictures though) but its style matches the back of the watch you posted.
http://www.swisswatchexpo.com/watch...er-Automatic-Date-Mens-3515-20-00-Unworn-6321
So likely legit - the dial is porcelain in the genuine ones, and this one looks like it may actually be porcelain to my untrained eye. But I'm not confident enough in that to actually recommend spending money on it.