When you have a large number of objects all under the same parent, the Build Control panel becomes extremely laggy.
In my scene, I have 2048 objects, each with a vrc_trigger. Switching to the build control panel takes 80 seconds and allocates over 2gb. Attached screenshot is a deep profile of the editor.
Sort of related, but disabling the parent of these objects "fixes" the lag. I assume this means that any checks the sdk tries to do ignores disabled objects.