I'm using Vegas Pro 15 on a HP Z820 Workstation running Windows 10. My audio interface is a Focusrite Saffire Pro 24 DSP.
This whole setup is new for me. Windows 10 was just installed clean. I installed the interface and got it configured in Windows with very little difficulty. The Saffire is set as default in Windows for both playback and recording.
When I am in Vegas, I can still hear the inputs form my interface, but I can't see them as options in the "Record Input" setting. Microsoft Sound Mapper is the only available option.