UPDATE: So I ended up routing wires from the lift-gate connectors located at the hinge line.
Camera In, Camera return, and Camera ground from the lift-gate connector to the back of the radio
D403 Line-bus from the lift-gate to I5020 connector under glove box for variable backup lines
F923 12V to the utility outlet. Originally I used the backup lamp circuit, but the camera wasn't getting a steady current (burned out bulb indication) and the camera flashed on and off. So, I rerouted to the 12V utility outlet.
I also, swapped the camera for one out of a 2018, I think I read it has slightly better resolution, but the 2015 camera wasn't sending any signal on the backup lamp circuit.
Bam! Everything works great now. I hope this helps someone out in the future because this was a headache.