Hey branskyj,
Ive got exactly the same problem as you. scene's are taking a long time to send through the network to the vrayspawner machines, and they dont kick in until half way through the render, it'd be great if they connected immediately.
It's no problem with smaller scenes.
I also believe it's a windows network speed issue. I just wanted to know if you've made any progress with this as im also after a solution.
your help would be greatly appreciated.
cheers !
Tom