The last project I used Eclipse on consisted of like 50 different maven modules. Plus we were also using a mix of Java and Scala code. The Scala plugin we were using seemed to make everything run very, very slowly. At times, it couldn't even keep up with my typing.

This was back in 2011 though. Obviously things have changed.

The difference between Eclipse and IntelliJ was like night-and-day, however, in terms of performance.