Audi offered 2 service plans, Fixed & Long Life.
Fixed is around 10,000 miles with the long life being double.
Lots of people say you should change the oil every 10,000 or sooner to ensure engine longevity.
There have been some issues with cars on the long life interval especially the 2.5TDi - mine was on the long-life interval from new, due to the age of the oil between services it caused the camshafts to wear, which sat me at a £1000+ bill to rectify.
You can never change your oil too frequently!