Reduce level 13+ build times

Upgrading buildings which are level 13 and above are disproportionately long. The time and money needed is exponential.
The difference between upgrading a level 11 to level 12 building and that building between 14 and 15 is huge. The time is the real problem. Working hard to gather the money takes long enough but can be excellerated playing matches (involved in game) but the number of days for the build is silly: you are locked out of that part of the game for days at a time (evening buying more builders doesn't help much). This waiting is frustrating.

You need to look again at build time at higher levels so no one build can be more than 2 days.
I think it's ok.
It is the idea of the game to take a considerable amount of time to get to the highest level buildings. For those having achieved 140,000 fans and all level 20 buildings the significance of the achievement would be taken away which is quite unfair.