Small Performance Drops In Busy Stations - Is It Cpu Or Game Optimization?

I have been playing Train Sim World for some time and I really enjoy it. Recently I started noticing something and I wanted to ask if others see the same.
When I drive into big stations (like ones with many AI trains and passengers), my game starts to stutter a little. It is not unplayable but I can feel small lag spikes especially when looking around or when many trains are present.
My system is decent (mid-range CPU and GPU) and the game runs smooth on open tracks. The problem mostly happens in busy areas.
So I have some questions:

• Is this more related to CPU usage because of AI trains? Or is it something about how the game is optimized in dense areas?
• Do settings like shadows, view distance or passenger density affect this a lot?
• Has anyone found a good balance of settings for smooth gameplay in stations?

I am trying to understand if I should upgrade hardware or just adjust settings better.
Would be great to hear your experience and what worked for you.