Using beta 8.09 three projects were tested, one with dozens of tracks, a second with dozens of edits and a third that ran 30 minutes. Playing or not playing made no difference on exit timing. It was instantaneous.
If they had been played but not changed, the "discard" warning appeared; this may be a cautionary prompt and is likely a good thing.
Effects and transitions were then added to the longest project. Exit results were the same. In each case caching was allowed to complete prior to closing.
Finally, the takis My_Den les kouventa was loaded and a half-dozen transitions/effects added. It was played to completion, then closed. Prompt appeared and was dismissed, but with no delay.
While a slow exit has been seen occasionally in the past, it could not be replicated in these tests. Specific PC hardware capabilities may affect this.