After 15 years = Five weeks 1 day
So 5 x 31 or 155 + for the weeks
another 31 for the 6th week of which 7 (roughly is accrued) and 23 hours POAL.
That's rough figures obviously. but my guess is POAL for 23 hours over the year is about right.
Ps. Also don't forget that on the year you change over from 1 entitlement to another, then your POAL is reduced pro-rata based on when your start date anniversary is. It's only the following full-year that you get the new entitlement in full.