For the record, a 31x10.5R15 is essentially a 265/75R15 - both tyres have essentially the same width and profile, but one is simply 1" bigger than the other (in round figures) because the rim is 1" bigger.
flexytj wrote:dont fix what isnt broken . your .31s are cheaper than the 16 inch metric equivalent too .
flexy does make a valid point, but you should also consider how you use your hilux. If it's a daily driver / weekend play toy / generally lightly loaded, stick with the cheaper 31s.
If you do long trips heavily loaded, the 16" version has significantly higher load ratings, so you're less likely to overload your tyres when you reduce the pressures. 31x10.5 is rated for a little over 1000kg per tyre at maximum inflation; depending on the tyre you buy, the 16" tyre will be rated around 1500kg per tyre. Fully loaded, you will be much closer to the load limit of the 15" tyre than the 16" tyre.
I will never tour on 15" tyres again.