The Kotlin compiler is slow, but if you break up your code into smallish modules and build with Gradle, it will only re-compile the modules that require re-compilation after changes which should make compilation times much shorter than 50 seconds.

At work, we have around 100 modules I think (some Kotlin, most Java though) and changing the API of the lowest level ones (used by everything else) usually causes re-compilation to take a minute, but as most changes are in the higher level modules (which are not depended on by anything else) and re-compiling those takes a second or two, it's not been a big problem for us.