Is there a way to tell what is the size of the download is between updates.  I believe only the delta is downloaded correct? Im downloading directly from Microsoft.

I tested on a machine which had the April version 15.0.4711.1003 and updated it to May's 15.0.4719.1002. When I watched the Download folder in C:\Program Files\Microsoft Office 15\Data\Updates\Download it was nearly a Gig of data.  That doesn't appear to be a delta but more like the whole install source.  Is this right?