I have a project open in Editor and it will only be built for Quest/Android (maybe later, for other platforms)
The OpenJDK Platform binary, which is instantiated when I switch to the Android platform in build settings, is consuming a lot of memory, forcing a memory-paging requests to slow my machine right down.
OpenJDK is used run tools when building for Android, such as Gradle. Gradle also has a service which is left running to make subsequent builds faster, it is probably it.
You can safely kill that process, it should be restarted on next build. However, it could be a bug in gradle that it leaks.