Coversion to keyless entry ?
 

Has anyone converted to keyless entry on a 2015 911? Cost?

I looked into doing this on my '14 Cayman for a while. The short answer is that it was easier to buy a car that had it already than to retrofit keyless entry to one that didn't.

I looked into having the dealership install an OEM system. (They wouldn't do it.)
I looked into buying a Porsche Entry & Drive parts kit off of Ebay. (It would have cost a few thousand dollars for the parts alone with no guarantee that it would work after another few thousand dollars of labor)
I looked into buying an aftermarket RF keyless entry and drive system. (Apparently, these can work with some of the older Porsche ignition systems, but not with the 991.X versions)

I ended up just looking for (and buying) a 911 that had all of the options that I really wanted. Best of luck to you. I hope that you have more luck than I did... but, I wouldn't get my hopes up if I were you.