Why is browsing the router user interface so slow?

Set the router’s TR-069 settings to use the Google STUN server.

For DrayOS 4 routers, go to System Maintenance, then TR-069, then STUN Settings. Select Enable and enter the following:
Server Address: stun.l.google.com or stun1.l.google.com (note that the figure before .google.com is a lower case L).
Server STUN Port: 19302

For DrayOS 5 routers, go to System Maintenance or Management, then TR-069. Choose the “More settings” option.
Select Enable, then enter the following details:
Server Address: stun.l.google.com or stun1.l.google.com (note that the figure before .google.com is a lower case L).
Server STUN Port: 19302