It has improved in recent releases, but I think they are focusing mostly on incremental compilation via the -watch flag. My projects still take 5-7 seconds to build from scratch on my MacBook Air.
You probably know this, but just for others' information: Type inference is expensive, as it requires global information about the project. As a result, compiling one TypeScript file in a project results in the compiler recompiling all of the referenced modules and definitions to re-build up that inference information from scratch. Using the -watch flag keeps the compiler alive with that information in-tact in memory, enabling incremental recompilation.
You probably know this, but just for others' information: Type inference is expensive, as it requires global information about the project. As a result, compiling one TypeScript file in a project results in the compiler recompiling all of the referenced modules and definitions to re-build up that inference information from scratch. Using the -watch flag keeps the compiler alive with that information in-tact in memory, enabling incremental recompilation.