I was reading this blog post about the experience of a team using Intellij Idea for large maven projects and have also looked at a similar question posted a
IntelliJ IDEA 2017.2 Added really nice feature, which helps a lot when working with large projects. Basically, you can mark which modules will be loaded by IDEA and which not. Unloaded modules will not be touched in any way by the IDE. They will not be indexed, searched, they will not be subject to refactoring on inspections. Loaded/Unloaded modules can be quickly configured in Load/Unload Modules dialog. The dialog can be opened using
Project Tree window → Right Click on a file → Load/Unload Modules...
Temporarily reducing the number of modules IDEA works with will greatly increase the performance for big projects. You can find more info about this feature and other performance tweaks for IntelliJ IDEA in a blog post I wrote: IntelliJ IDEA Tips & Tricks: Improving performance