When the file size for Wolfenstein II was first listed on the eShop, in came in at 13.7GB. Now, however, that has changed. The official listing has Wolfenstein II down for 21.8GB.
The updated file size was somewhat expected. Earlier in the month, the eShop page added in a notice stating that a microSD card may be required to download Wolfenstein II. The message further mentions that at least 23GB of free space will be needed to download the game upon release.
Source: Switch eShop