Just ran into this issue myself for the first time. All of a sudden the whole IDE became very sluggish. Waiting 2-3 long seconds, just clicking from one method to another. Or from one button to another. Quite a mystery at first, but I figured out my problem. I doubt it will solve this whole issue, but here's what I discovered.
Saved as a binary file, my project has been in the 200k area. After the sluggishness started, I noticed my project size had grown to over 1 meg. I've been working with some large JSON files. So to save time, rather than going out to the server for a fresh download during every test, I put the JSON data in a textbox. Turned out that was the problem. As soon as I deleted the text box, (with had a huge amount of test data), the IDE once again resumed its normal response time.
My best guess is this: internally objects are not stored a relational manner and thus, every edit may require rewriting the a large portion of the app internally in memory. If this is true, then the larger a project becomes, the more an issue this is.
Maybe rather than updating the app (internally) with every click and keystroke, it might be more efficient to update only when switching from one object (window) to another. So the delay would only happen when switching methods, not when typing code, or changing focus from one button to another.