Tyre pressures advice needed

Picked up a new van from the builder in July and "assumed" tyre pressures were OK. Having done 3 trips in 6 months now just checked wheel nuts again and tyre pressures for the first time on the weekend – I have one tyre at 48psi and three at 46psi. I would have thought these are too high – can I have some advice about van tyre pressures please. The van is a 21’ triple bunk with ATM of 2250kgs. It runs 15" light truck tyres on alloy rims.

Michael Kelly, Mt Cotton