i guess that technically breaks don’t count towards duty so in theory 15 hours duty isnt possible as you would need to be at work for more than 15 hours. 45 min total break is possible for a 15 hour shift if you do less than 4.5 hours driving but who would want to.
years ago i had a warehouse job where 12 hour shifts were the norm for some and they would have 45 min break (1 half hour and 1 15 min break)
For the RT(WT)R all shifts over 9 hours working time require you to have a total of 45 minutes break.
The break can be split into breaks of no less than 15 minutes.
As long as you do not go over 6 hours working time without a break of at-least 15 minutes the break/breaks can be taken at anytime except the immediate start or end of shift.
Breaks for the RT(WT)R have to INTERUPT the total working time that’s why breaks at the immediate start or end of the shift do not count for the RT(WT)R.