[hocuspocus]

Firstly, IDEA's default JVM settings are a bit conservative. The default 750MB maximum heap size is too low for any non-trivial Scala project. Here's someone who attempts to explain all settings: https://github.com/FoxxMD/intellij-jvm-options-explained

Secondly, IDEA's SBT plugin works pretty well, use it if that's not the case yet, and put a reasonable .jvmopts file in your project. SBT can still be slow and there no magic cure for that (even though it's constantly improving). Some of my coworkers use bloop instead: https://scalacenter.github.io/bloop/

That said, Scala is indeed jumping on the LSP bandwagon, and it's already supported by Dotty out of the box.