I'm using IntelliJ on Windows for Scala dev, and boy is it slow. I have to manually set the process priority to "Below Normal" every time, or it will soak up all system resources and music playback becomes jittery. Clicking right on anything is a four-second pause mistake. It's free, so I shouldn't be complaining. Thanks for the product! Really, it's better than vim (especially with the intellij vim-mode plugin). I a…
At home on my desktop (4Gb of ram and a HDD) I switched to Emacs + ensime. It has a subset of the functionality of Intellij (some refactoring, jump to definition, type inference, autocompletion) and Emacs commands are hardwired in my brain. It's lighter than Intellij, you could check it out (and add some vim emulation since you seem to be a vim user!)
edit: there are ensime integration solutions for vim ( eg: https://github.com/megaannum/vimside )