Do you track time so rigorously in your game that the difference between 5 and 15 minutes is meaningful? Do the chances of wandering monsters change between these two? I think in most games the answer would be no to both of these.
I'm mostly running pre-made adventures - Princes of the Apocalypse, to be specific. Random encounters aren't really a thing in most of the dungeons in that adventure except in particular places with lots of traffic. However, they are inhabited dungeons, so people in nearby areas may respond to sounds of battle and such - either by entering the original battle, or by preparing for intruders somewhere else. That's mostly something I base on my own judgment.