While this quite likely won’t be necessary, you may want to read up on how to mount remote shares at OS level:
If you decide to do this then you get the operating system to mount the remote share as if it were a local folder, and Kodi then thinks it’s reading from within the root file system. Doing this will result in faster data transfer - but obviously you don’t need data to be transferred from the NAS faster than the maximum bit rate of any of your videos, so it may well not be necessary.