Thank you for your reply.
I have checked every possible setting, including power saving mode. I also checked again with the technician at the shop were I bought it and he confirmed the lag.
The conglusion is that if you disable the autofocus you have a smooth evf. The autofocus need a lot of CPU and that causes the evf to lag. Unfotunately I had to return it back because of this. The viewfinder is very critical for me and I can't ignore this problem.