Hi Denis,
There could be a lot of factors that affect X-Plane in this case. It could be that the scenery is more detailed around London and X-Plane is simply doing more work behind the scenes. Anytime X-Plane has to create something it could cause it to slow down. Loading new scenery tiles, having a lot of AI aircraft, etc.
I'm surprised that you say it's "stuttering" without losing FPS though. Are you using any third party scenery, plugins or planes? Same weather settings as in Slovenia?
It's very hard to diagnose & troubleshoot stuttering or FPS drops unless every single factor is the same between tests (location, view, rendering settings, plane, weather, everything).