Updating the wireless adapter driver seems to have solved the slow wifi issues that are apparently plaguing other users as well (sub 2 Mbit/s when all my other devices are getting ~80 down). Unfortunately, ASUS doesn't provide the latest wireless adapter drivers on their site, Windows claims the drivers are up to date, and Qualcomm doesn't provide drivers directly to consumers (a questionable business model). So, I searched around and found updated drivers for the Qualcomm Atheros QCA9377 wireless network adapter. The driver version I was having issues with was version 220.127.116.11X (I don't remember the exact number). I installed driver version 18.104.22.1685 and my wifi issues have vanished.
Here's where I found the new driver (note that this is for 64 bit Win 10, although I assume that's what we are all using):
I followed the instructions as listed on that page. I used 7-Zip to decompress the .cab file.
Hopefully this fix works for others who are getting unacceptably slow wifi.