Nokia Lumia 820 - How long does it take to scan the memory using Storage Check on my Lumia device? Why does it take so long?

Storage Check scans the entire filing system and may take a while, up to 40 seconds when the memory is full. There will be a spinning animation in the overview display indicating the ongoing scanning process. Once the scan is complete, a visual representation of the memory is displayed.For further details please see the details view.