Update:
Hello, fellow pilots,
I have good news. I've resolved the issue.
The problem was caused by a third party Vienna city scenery which was too heavy for system to handle, that's why it was only doing on LOWW. After removing it, I completed a flight (Warsaw - Vienna) with Fenix A320 and everything went smoothly, FPS were great, like on any other airport. There is still a bit of small stuttering, but it's totally flyable.
Anyway, I would like to thank you for your help, I really appreciate it.
Happy and smooth landings.
Cheers!