I have a reply from Leif, and I will paste it verbatim.
“Applying QoS to packets in windows is very difficult — in fact not always possible, as far as I know, depending on windows version and permission level.
There’s also different types of QoS, differently flagged in packets.
The code does attempt to do it, if you’re running as a service, so that BA has admin priviliges, which is actually required.
Can’t guarantee that it succeeds, though. If that’s really important for his particular use case, he may want to configure his network switch to do it.
If he has a switch that cares about QoS to begin with, it can be done there. If his switch doesn’t care about QoS then his question is moot.”
So, are you able to configure QOS in your router/switch? That may be the best option, as it ensures you have direct control over it outside the application.