The only versions Apple is signing on Facebook in that range is in the pic attached. 3.10 is the closest, it appears. I can downgrade to any of these versions, and that is only possible if your phone is jailbroken on iOS 9.0- 9.0.2, and the app "App Admin" is download and used.
Edit: I downgraded to this version to see if my 64 bit 6s Plus system would work, but it crashes and gets stuck on log in screen.
Version 5.0 seems to be the oldest version compatible to newer phones. As seen in pics, it's not formatted to fit IPS6+ screens.