IMHO, every 5,000 kms or 3 months, whichever comes first.
Degradation of oil starts as soon as you pour it in the engine. It may be less compared to a similar vehicle which is having bigger mileage but still the properties are still changing brought about by oxidation.
Another IMHO, if the operating and maintenance costs of owning a vehicle is a little bit on the upside, I beleive its better getting rid of it and invest the money somewhere.
Practically speaking a vehicle should serve its purpose, it should be a necessity, if it is not, then it is a liability.
