Holden changed their recommendation from 10,000Kms 15,000 Kms. (In order to compete with some european brands.}
Then when you go in with a problem they tell you that the fine print says "under ideal conditions" or similar words.
(That is non stop long distance highway driving.)
I am told that the new (VE onwards) motors have some very fine oil passages that can block or build up "plaque" so if you carry heavy loads, or drive in stop-start or hilly conditions you need to increasingly adjust the oilchange frequency.
Full synthetic in good brands can be had for less than $6/litre if you wait for a sale and good filters under $10 if you buy a few at a time.
After my daughters VE engine was destroyed at 160K by a sticking valve I do my LY7 between 5K (Metro) and 10K (Country) - not towing.
It is good insurance.
ps Change the diff oil.