Hello Clintwade,
Welcome to Microsoft Community.
I believe you must be using this Dock:
But let me show you the data transfer speed corresponding to each port:
If you access port 5 in the screenshot, that is an Ethernet port, and it actually supports a transmission speed of only 2.5Gbps(that is 312.5MBps). So it can't get to 1.5Gpbs anyway.
I know that you have confirmed with your ISP that the network you are using is 1.7Gbps, so this means that the network should be 1.7Gbps when you access the Shaw Router XB8 router. At this time, you need to find a way to test whether the Ethernet transfer speed from the Shaw Router XB8 is only 150 Mbps. The Surface Thunderbolt™ 4 Dock does not reduce Ethernet transmission power unless this is due to the router's own limitations.
Best Regards,
Mitchell | Microsoft Community Support Specialist