15+ hours and reduced rest

Well yes, the answer is that once you’ve failed to have a qualifying daily rest period your driving time will keep accumulating until you do complete a qualifying daily rest period or a weekly rest period.

The EU guidance is that when you fail to have a qualifying daily rest period, the period of 24 hours is reset as soon as you’ve completed a rest period of 9/11 hours, unfortunately I don’t see anywhere that suggests that the daily driving time is also reset.

The definition of daily driving time is the driving time between daily rest periods or the driving time between a daily and weekly rest period.
As far as I can see the only way to reset the daily driving time is to have either a qualifying daily or weekly rest period, i.e. a daily rest period completed within the period of 24 hours from the start of the shift.

GUIDANCE NOTE 5 (europa.eu)