In the rotated boxes video https://www.youtube.com/watch?v=Oz98L4Fyxoo at 15:13, Uncomfortable says "...don't be alarmed if it still requires you to allocate additional time when this exercise comes up in your pool of warm up exercises."

The observation exercises are a different ballpark but based off that, I would assume that you would exceed the 15 minute limit to give you sufficient time to observe and put at least some marks down. You don't have to finish it in one sitting.