At 16m you can dive with Nitrox40 (oxygen enriched breathing air with less nitrogen) and the ground times will be mainly limited by fatigue and body heat loss.
At 16m or even to 50m...you can dive supplied air however long you want....
We have ROV's that can map an area, with video, sidescan, mag, and sub-bottom profilers...mowing the lawn for weeks...
Most have a recovery arm....