Why is IntelliJ 13 IDEA so slow after upgrading from version 12?

I had the same problem with slowness in IntelliJ 13 after upgrading from 12. What worked for me was editing the idea64.vmoptions in the bin folder and setting the max heap to 8 GB (was 512 MB) and the Max PermGen to at least 1GB (was 300MB).Example below:

-Xms128m
-Xmx8192m
-XX:MaxPermSize=1024m

Upon restart it was much faster.

For IntelliJ 2020 going back to 2017 on Mac /Applications/IntelliJ IDEA.app/Contents/bin/idea.vmoptions

On a Mac, this file is located in this path:

For IntelliJ 14 or 15 on Mac /Applications/IntelliJ IDEA 14.app/Contents/bin/idea.vmoptions

For IntelliJ 13 on Mac /Users/yourusername/Library/Preferences/IntelliJIdea13/idea.vmoptions

IntelliJ's updater (since 2017) seems to roll this change back, so you may need to re-apply it after updating.

On Ubuntu Linux, this file is located in this path relative to the install directory:

idea-IU-135.475/bin/idea64.vmoptions

and for 2016.2:

 ~/.IdeaIC2016.2/idea64.vmoptions

On Windows 10 (Community edition shown here) these files are located in:

C:\Program Files (x86)\JetBrains\IntelliJ IDEA Community Edition 2016.1.3\bin\idea64.exe.vmoptions

I noticed that disabling many of the plug ins really helps speed up IntelliJ. For example, I am not developing Android Applications. Turning the plugins related to Android development off speed up load time and makes the program run much smoother on my machine.