A Flight Instructor reported they descended to 150 ft over a populated area.

Narrative

During a demo flight I flew directly over the clients house. Due to Class Bravo airspace directly above me; upon takeoff I elected to keep a lower altitude to ensure that when I gave controls to the client; we would remain outside the Bravo airspace should we inadvertently climb. Over the clients house I took controls back and put the aircraft into a slip so that they could take a photo of their house. I remained cognizant of my altitude above the houses and estimated that i was still approximately 600-800 feet above them; which is all I was able to maintain do to the Class Bravo airspace above me. That's when I noticed foreflight said I was only about 150 ft AGL. I looked at my altimeter and saw that it was reading 5300 MSL. I immediately exited the slip and began a climb back to 5600 MSL. It did not appear to me that I was only 150 ft AGL. We then continued our flight southeast and had no further incidents. I think the problem was cause by trying to please the client and show them a good time in order to gain business; mixed with the pilot's inadvertent loss of situational awareness.