Increasing Memory Heap
The Java Virtual Machine (JVM) running IntelliJ IDEA allocates some predefined amount of memory. The default value depends on the platform. If you are experiencing slowdowns, you may want to increase the memory heap using the corresponding JVM option. For more information, see Configuring JVM options.
On the Help menu, click Edit Custom VM Options.
-Xmxoption to a higher value and restart IntelliJ IDEA.
IntelliJ IDEA also warns you if the amount of free heap memory after a garbage collection is less than 5% of the maximum heap size.
Click Configure to increase the amount of memory allocated by the JVM.
Click Save and Restart and wait for IntelliJ IDEA to restart with the new memory heap setting.