The best way to find where the problem is without using test gear is by the process of elimination.
Test you LAN using LAN Speedtest. First test using Ethernet connections and see if you can get speeds of 90+ Mbps. Much higher is possible if the equipment you are testing with has gigabyte capability at both ends.
If you can't 90+ on your LAN there is a problem with your LAN setup that needs to be addressed.
Then you can test speeds on your LAN using WiFi.
Using Speedtest introduces to many additional variables making it very difficult to diagnose throughput problems.
Once you know that your LAN is up to standard then you can point at Verizon.