How does one get a 500kg horse into a trailer truck?? Right let it walk up a ramp.
One could think of the same for a bike. 1.5 meter is not that high and I assume the truck living unit will be some 2 meters high which gives you a 2 meter ramp length already. If you can think of extending the 2 meter by using a double hinge with a ground support in the middle, giving you a 4 meter ramp, then you will have a moderate angel (22 degr) and sufficient width to drive the bike in (approx 0.8 meter; the width of storage area is dictated by the width of handle bars) and out backwards with brakes engaged. Or, if you want to go really crazy, have the same set up on the other side too so you can drive one side and out on the other side.
You will need some solid gas dampers on the door and some anti slip surface, like the horse trailer. Actual seen a setup like this where the bike was stored outside between cabin and living unit. The ramp was a loose steel ladder. No need for complex constructions.