Makes sense - I think a lot of it comes down to playing with the emissions figures and meeting the euro 6 requirements over practicalities of driving.I guess you are very close to the tyres maximum load. Most tyres have to be run at maximum pressure to achieve maximum load. The down side is that everything about a tyre is worse at that kind of pressure.(other than economy) I am carrying a similar load to you on 235/60/17 and running safely at around 40psi. I would strongly recommend changing to 17" wheels and tyres (235mm wide) when you can. There are loads of Devonport vw t6 wheels and tyres around (brand new-delivery miles) for around £600, which is an absolute bargin. It also relates to the tyre pressure = the ground pressure which equates to the load you are carrying; so narrower tyres need greater pressure