Ok so try this...
On your windows computer, open the network preferences and go in the in the wifi settings, ipv4 and try to change the DNS to 8.8.8.8 and 8.8.4.4 test again for speed.
Open Network and Sharing Center
Click on WiFi then Properties
Ipv4... On the window that appear select that you want to use your own dns..
Does it works faster?
You may want to disable also ipv6 and that some times improve the speed when using cellular connection.