Something fishy is going on here, but we aren't quite sure what it is yet. File size info on the Switch version of Mortal Kombat 11 has surfaced, and it seems the base game is just 6.54GB. That would be great news if there weren't also a 15.9GB day-one update.
There's a few things we don't know about this update. First off, we're not sure what the update does. Second, we don't know if there's a day-one update on the other platforms. Third, we don't know if that update is necessary to play the game. This might end up being a situation where Warner Bros. decided to go with the smaller 8GB game card release for retail, and then took 15.9GB of necessary files and made them a day-one download.
Whatever the reasoning, just be prepared for some extra microSD card space if you're grabbing Mortal Kombat 11 on Switch.