Now that tsc compiles most of the plugins in the bootstrap stage, it has started to take quite an impressive amount of time.
There are still several options left to improve the situation:

• do not compile test files
• do not compile big json files
• debug tsc to identify other bottle-neck or unnecessary work Debugging long check times with TypeScript? microsoft/TypeScript#24435 Build watch takes 30x as long as cold build, high transformTime microsoft/TypeScript#35729