I had a 2003 Range Rover HSE with the 4.4L BMW engine. I got 18 MPG on long drives and 12-13 around town.
I can definitely imagine getting 22 MPG with a diesel. Hopefully you'll get someone with experience with that engine.
My BMW History: 1979 BMW 320i | 1997 BMW 328iC | 1998 BMW M3 | 2003 Range Rover HSE | 2007 Range Rover SC |2010 BMW ???