There’s a little bit of tolerance, but it depends on what the problem is.
If for example you stretch every service out to 17500km and have a problem with something that would never have happened if it’d been checked or the oil replaced at 15k km, then you’re out of luck. But if you let one stretch to 17.5k km, then the next one was at 12.5k km, and then not long after you had a problem ... well most likely they’ll opt to cover you.
But if you let two successive service-intervals run to 17.5k kms and then something like a piece of interior trim fell off, well they’d cover that ‘cos your stretching the services wouldn’t have affected it.
It’s really very much best for the car if you don’t let it run so long, though, regardless of warranty.
It also helps resale if you’ve had the car serviced properly.