At first I would try sbt-tmpfs, and then the largest factor in compile time imho are dependencies. Make sure that you split your project in submodules of semant

At first I would try sbt-tmpfs, and then the largest factor in compile time imho are dependencies. Make sure that you split your project in submodules of semantically valid units. That reduce the amount of code that has to be analyzed. And then make sure that you don't have many unused imports. In every project I've been are some former Eclipse users that are accustomed to collapsing all imports and adding new ones automatically. They never look at their ever growing list of unused files that are searched, loaded, and parsed.