Is it always high in speedtests? https://speedtestfast.com/xfinity-speed-test-online.png This is not normal. Ping your private gateway to see if your local network is slow. Then ping your WAN gateway. If you log into your router you should be able to see that on your broadband/wan tab.
Both of those pings should be around 1ms or <1ms
Can you list out of the devices going from modem to your pc? Only ethernet cables have consistent performance.