Consecutive 15 hour shifts, over 2 different weeks?

Terry Cooksey:
Can’t do it, as reduced rest periods count in the ‘working week’, not the ‘fixed week’, ie, between the end of one weekly rest and the start of the next.
Also, how can you work 3x15 without reducing rests? If you work 15 hours, then rest for 11 then you will start day 3 4 hours later than you started day 1, meaning in the 24 hour period from starting a shift, you will not be able to fit in even a reduced rest of 9 hours?

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I’ve not done 15 hours, but have gone over my 13 hours. Start times are not fixed. Started at 3:45 on Friday, and will start at 7:45 tomorrow.

As I understand, 13 hours and 1 minute counts as a 15. I refuse to take a 9 hour rest.

Shifts have been 3:45-17:45, 5:30-19:00, 6:15-20:40.

So tomorrow, I start at 7:45. The latest I can work to is 20:45?