How the heck do you sketch a realistic environment in only 15 minutes?

My professor gave us a sketchbook assignment to sketch an environment from life in 10-15 minutes at home. I never understood how tf people can do this. I mean I know obviously it’s not gonna be fully rendered, but how does anyone produce something even remotely coherent in a non-cartoon style in under 15 minutes? You’d pretty much have to make 0 noticeable mistakes that throw off the drawing, at least in my experience