There is no data that suggests that the published service intervals are a problem, no matter how long you plan on keeping it.

I have moved from 5000 km changes many years ago, to 8000 km, to 12,000 km, and now to 20,000 km+ on the last two vehicles. No issues whatsoever, no increased oil consumption. The oil stands up. The filter is good for two year intervals.

You may decide to do it more frequently out of an overabundance of caution, but you don't necessarily need to go form 20,000 to 8,000. And once a year is a good target, not once every six months.

You may want to look on the Australia forum on this site because intervals can depend somewhat on local fuel quality.

What matters most with the diesel is the fuel filter change interval, IMO.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue