Documents with a lot of embedded macros or print-resolution images can take a very long time to load. A lot of businesses load up Word documents with pictures and logos for brochures, and Word has to process all of those images before the file opens. Word documents with links to such images might therefore have long open times. This is especially true if you've configured Word's Zoom feature to display many large images at once.
Thanks Lennart for providing such detailed information! The boot perf issue only occurs on HDD where loading fonts are slow, especially in the case that there are a lot of fonts to load. Here is the major differences between Mac Office 2011 and Mac Office 2016 that contribute to the issue: 2011 is not sandboxed application, and all the Office fonts are installed in /Library/Fonts/Microsoft that are accessible system wide. But 2016 turned to sandboxed, that such fonts locates inside application bundle that system has to load on every session, and HDD is not efficient at that. We are proactively working on this issue now, and will keep you updated when it is fixed.
Again, thank you very much for the valuable feedback, we really appreciate it! -Harry.