Hi Tobias:
Thanks for your answer. I use 12 computers and the bandwidth not exceed 5Mb in the worst case, all processors in the master runs below 1%. Changing the screen update not affect the behavior. Unfortunately I need to downgrade to iTalc, veyon it's unusable for me.
Edit: I install iTalc again and works ok. If I change parameters can't reply de Veyon behavior but if I choose iTalk demo internal server everything work slowest. Maybe this can help you to detect the problem.