If you’re using the default settings, you’re connecting to NetSpot’s servers over your internet connection, which I would expect to be far below 150 mbps.
Halfway down this article they discuss using self-hosted PHP scripts, which would let you test throughput on your LAN: /help/active-scanning/
The PHP scripts themselves seem to be available from this page: /help/edit-servers-download-upload-speed/
You can also use iperf3 locally.