Oil Change for Longlife Engines

I have a TDI engine with long-life service intervals installed in my T3 van.
Der Geschwindigkeitsanzeiger ( stammt aus einem Golf IV) bekommt über die Tachowelle und dem org. Hallgeber ( ist an die Welle verbaut) sein digit. Signal.
The speed displayed on my speedometer is approximately 50% lower than the actual speed I am traveling.
The odometer will only display half the actual distance traveled.
What impact does this false warning have on my oil change, which is supposed to be indicated to me on the display at some point?
I have driven approximately 25,000 kilometers (about 15,500 miles) in the last 2 years, and I haven't received any warnings so far.
Let's assume, for the sake of argument, that with normal mileage, an oil change is due every 30,000 kilometers.
Does this value double with my 50% false positive rate?
Perhaps someone can also tell me how I can double the signal?
Best regards, Hoin.