Downloading the Current EFI for the 2015 MacBook8,1 Model?
EFI updates are available from the command line:

softwareupdate -la


This is the same information as the App Store app shows. The tools check apple's entire catalog and then calculate locally if any updates are required. You likely are up to date, but this is how to check. 


https://support.apple.com/en-us/HT201518