I see that Threat Analysis (Snort IPS/IDS) is enabled on this site. Threat Analysis in configured in the Firewall > Threat Analysis section of the Portal . This means to accurately run a speed test for the entire network you will need to run speed tests on at least two machines at the exact same time. Below is a video that explains this.

The 150Mbps is due to the multi core processor that is running the inspection where each instance of the inspection will pull between 40-75Mbps where there are 2.5 cores running. To excite each core multiple connections have to be established. To get the throughput of the entire network you will add the values from the different machines together for the total network throughput.