We are working with Scala at that scale at Foursquare, and compilation times are definitely a headache. What helps is ensuring your dependencies are acyclic so you're able to do smaller incremental compiles when you make changes. To get us on the path of a DAG-ified codebase, we've been using a build tool developed by Twitter called "pants":

https://github.com/twitter/commons

which has some similarities to Google's Blaze build tool.