I doubt that sort of replacement would work. The S6 camera has some flash memory and a dual axis gyroscope that the front camera on the 2014 Moto G doesn't have. So even if the connectors are the same, you're looking at different length ribbon cables and just a different way that the camera fits into the phone. Those chip components on the S6 camera might be squished/damaged if you try to install them in a 2014 Moto G.
It's a shame, too, because it'd be awesome to be able to upgrade the camera on my 2014 Moto G.