[Joky]

Something smells with the structure of the project if a small change in a single file triggers a long rebuild. Including headers that define template should be "free", it is costly when you start instantiating all of them. There might be opportunity to restructure some part. Also precompiled-header or better: modules can help (not much with template instantiation though).

[dibanez]

In my parent comment are listed compile times from scratch, although there probably exist one or two files that would trigger similarly long rebuilds (included indirectly by most other files). If you change a random line of code, chances are the rebuild is quite limited. As others commented above, this actually scares people away from improving the core files.