Here is the thing.
15 years works fine for the politicians. In 15 years time, they will have either been voted out of office, or they will be Robert Menzies, Franklin D Roosevelt or Otto von Bismarck. Either way, it will not matter.
Consider, though, the situation of the regular, young ambitious bureaucrat. The London 2012 Olympics came along. It was a short term assignment, but if you were 22 in 2008 that did not matter that much as you had few long term commitments. So, you decided to do stuff for the London 2012 Olympics.
If you were really smart, or really avaricious (or both), you figured out that there is a permanent, extremely well paid career (with virtually no accountability) running the Summer Olympics (wherever it is that they are held) for the next several decades, and went for that. If you were not quite so smart (or if you had delusions of patriotism) you decided on a British public service career instead. The time at which you may be reaching the peak of your career (department head, or possibly the place a little below that where you do the actual work) will be in about 15 to 20 years. This is the moment at which you will not want the facts about the sheer level of waste and excess that went on at the London 2012 Olympics to become clear.
So, my guess. In 15 years, it is still going to be very hard to find out what the 2012 Olympics cost, and who exactly spent the money, and what it was spent on.
(Try finding out what the Sydney 2000 Olympics actually cost. As the years have gone by, the reluctance of the people involved to give out actual information has got stronger rather than weaker).