The service indicator on my 2015 plate octavia tells me it needs a service in 3800 miles. I usually service every 10,000 which means the warning is on nearly 40% of the tome the car is driven.

is there any way that you can get it to warn you at say 15,000 downwards ?

Well, on fixed intervals earlier cars only started the countdown warning at 1_000 miles or one month to go.

It sounds like last time at the service it was on Variable / Flexible servicing and not reset properly, 

so has still variable set for the Oil Service or Inspection Service which really is the same things at the same time.

 

If you do want 10,000 mile service intervals get it set on Fixed servicing. Not 10,000 miles though, that will show 9,400 or maybe 9,600 / 372 days.

My countdown appeared at 2000 miles (on variable), 4000 does seem a lot, especially if you're on fixed.