You aroused my curiosity so I did away with my Wows game folder and downloaded a fresh game with a Casio stopwatch running.
From dl start to Play for 18.xx GB was 10 minutes and 30 seconds.
Now, I use Cox Cable with their Gigabit service, my router can handle Gigabit speed from the internet and it connects to a Gb ethernet hard wire network to my Win 10 gaming computer.
Even if I dropped my bandwidth to 50 mbs it would take less than 4 hours to install a new game.
I looked and Wows stores its' download in the updates folder inside the game folder.
All of my games are kept on a separate ssd and not on the OS drive.
How is your internet, network, and computer set up?