DISCLAIMER:
Not sure about your 2015 model… but here are photos from the schematic of my 2013 Voltage 3200. One could hope, and probably assume that they use the same type & size… but we all know from experience that isn’t always true. So with that out of the way…
Contrary to the note highlighted in my 3rd photo stating that “all hose is 1/2 ID unless noted”… by matching up the Materials List (2nd photo) with the line run drawing (4th photo), it appears that ⅜ is used on my long-run pipes throughout the rig… with ½ inch only used between the intake & water pump, and again from the intake to the fresh water tank (final photo).
So again… take from this what you will. Good luck!