Does your account have Smart Browsing (some don't)? Of course, normally Smart Browsing isn't this fast when downloading a large file, but it may just like you. LOL.
I had to manually update my laptop due to the Anniversary Update not working through Windows Update, but I know that they are staging it, with newer computers receiving the update before older ones.
You may also want to consider disabling SmartScreen as well then.
Does SmartScreen use a lot of data, "a lot" being relative?
I use Webroot. It used 150MB last month, but there was a program update. I think it normally uses less. Used to use Avast, but I needed something more amenable for my folks' dialup PC, and it was $1 more for three computers versus one computer, so I have Webroot on two of mine.