It seems that the software updates for Office 2016 for Mac are pretty big. Around 500MB per update per application. This means, on average, a 1.5GB download for what essentially should just be bug fixes.
Come on Microsoft, get your act together and start offering in-place updates! Office 2011 did this, downloading 150MB or so per update and then launching an updater to patch the files. It’s totally unnecessary to download the entire Office 2016 suite every time you update it. Not everyone has fast internet, and many people are still on capped data plans.