If those 15,000 people were going to retire at 55 as they couldn't put more into pension (so it paid to retire) - how much income tax would they return over an extra 10 years of work?
I think quite a lot of professions suffer from workers retiring early because they've maxed out their pension, taking their accumulated knowledge and skills with them. I have friends and relatives who have done exactly that (civil service/doctors/police)
It might make economic sense as well as help retain workers.