NB: IDEA performance is improved drastically by giving it more memory. Basically every time someone complains about perf issues with IDEA it's because their heap limit is too low. It can be configured via the help menu.

One of the unfortunate (or fortunate?) design decisions in IDEA is that there's an explicit and user configurable tradeoff between performance and memory usage, but the defaults are far too low. And if it's too low only the most very recent versions can detect this and tell you what to do about it.