downloading from steam 38 MB/S
downloading from origin 37 MB/S
downloading from battle.net maximum 6 MB/S and average 4 MB/S
Hello Toxxins 
Unusually slow download speeds are in most cases caused by some sort of software conflict or by certain network settings.
Would you mind restarting your system in a selective startup mode and also make sure your proxy settings are disabled?
Just to be on the safe side, I would like to also ask you to make sure you have no bandwidth limits set in the App:
- Open the Bnet app
- Click on the Blizzard logo → Settings
- Go to Game Install/Update
- Scroll down until you see Network Bandwidth
- Make sure the value for Latest Updates is set to 0