It’s one of those grey areas where you have to make the judgement, almost certainly lightly loaded since the van in a empty state would be considerably lighter, if your conversion was based on a van but I would presume the conversion was done to a people carrier or MPV that could possibly seat 7-8 people and their seats.. I know from experience that those seats are very heavy, my old V280 had 5 removable seats that we often shuffled around.
If you have a kitchenette and a double seat in the back, add the roof bits and two passengers you are probably still only moderately loaded + luggage, a awning a couple of bikes on the back and some surfboards on the roof then maybe you should consider it fully loaded.
All of this is tyre pressure guidance is subjective really since tyre wear should be dictating tyre pressures, the supplied recommended guidance is simply that. I would stick to what it says on the sticker it will be pretty close to your optimum pressures, this changes with different tyres and temperatures. Assuming your tracking is good, high pressures will wear the central section and low pressure will wear the edges (equally).