So I looked at the 2012, 2013, 2014, and 2015 service manuals and compared all the base model unit harness pinouts, and I was reading the 2015 diagram upside down...
Even though the 2015+ base HU added the phone/usb/bluetooth interface -- the pinout for master power, acc power, and illumination is all the same. These are the major things you would need adding an aftermarket HU. Think most people run new speaker wire, but you could even use the stock if you wanted as that pinout is correct as well.
So anyone wondering about 2015's on up with the base audio -- the Metra harness will work.