You don’t have to do high mileage to keep new diesel engines in good condition, all you have to do is once in a while take a trip on a motorway/dual carriageway in a lower gear than normal to keep the revs higher and heat up the exhaust system for 10-15 minutes to give the DPF enough time to burn off the excess carbon build up.
The OH has had a diesel for a few years but only does very short trips in it, once a month I take it up and down two or three junctions on the local motorway and back and that has kept it in perfect condition.