Could be several things, including Onedrive syncing, Microsoft account syncing, Office syncing, and of course, might actually be the Surface Pro 4, and interference around it.
The Ping is most suspect at the culprit being sync activity.
Okay.
I have a few MacBook machines, and also insist upon fastest speeds for them, and my Surface equipment. I have found that some WiFi channels are faster on the Surface Book, and some faster on the MacBook Pro 15 Retina.
So try reconfiguring your WiFi.
If that has no effect, try uninstalling your Network Adapter from Device Manager and cold rebooting.