Discool's answer, "As slow aspossible, as fast asnecessary" needs a little explanation.
"As slow aspossible", so a warm engine doesn't stall or become lumpy on tickover. That's applicable to all cars.
Where things are different on the Landy is in how fast is "as fast asnecessary". In 1st High, the engine tickover of the 2.5 N/A Diesel should creep the truck forward with your feet off the pedals. A slow forward creep, on flat ground, just enough so it won't if on an un-mettled road, is what my REME trained dad says.
Alternatively, you could fit a hand throttle, so you can 'tune' the tickover to allow you to creep when off roading or when you want slow creeping capability, and just set to "As slow aspossible", so it doesn't stall in normal road use.
Rick