Use Android/iOS device as your PC's microphone, using Mumble + Plumble. Or use microphone of one PC on other PC.
Linux-only script, but steps can be replicated on other systems (e.g. using VoiceMeeter).
This is the lowest latency I've ever achieved (sounds almost like local loopback, theoretically 7ms WiFi delay + 2x 10ms codec delay = 27 ms).
Install Mumble (desktop client) + Murmur (server) + Plumble (Android/iOS client). Set all 3 programs to use best quality and minimal latency. Set mobile client to always streaming.
Copy mic_over_mumble anywhere - it will use ~/.mic_over_Mumble as configuration directory.
Run mic_over_mumble, then connect your mobile device to LAN server.
Then, set up your programs to use monitor of Mumble as input device. E.g. in OBS:
