Performance issue people are having is simply the game and how it handles your moden hardware and software running it. Notice that you never use more than 10-20% of your GPU power and usually no more than 50% of one CPU core.
The game runs differently for everyone. People with the newest I9 and a RTX 2080 SUPER can lag while people with 3rd gen I7s and a GTX 670 (What i have) have no issues. Or it can be reversed. The game is a fickle ♥♥♥♥♥.

There are ways to mitigate the issue for some people but may not work for everyone which i will explain here.

-Using the Task Manager, go to the details tab and find StarWarsG. Right-Click and click Set Afinity. Then set it to use only 1 core or if you have a hypertreaded CPU 2 "cores"
-Again in the Details tab of the Task Manager, Right-Click StarWarsG, under Set Priority set it to HIGH.
-Turning off ALL overlays. Windows Games, NVIDIA, Discord, Steam.
-Turning off Bloom and Heat Distortions ingame.
-In your GPU's Control Panel turn off or set to lowest everything you can because this is a old game and new GPU features it cant use can cause issues for some people.
-Play at 1080p
-On the game's exe file try setting it to various compatibility modes.
-Play Windowed
- If on a laptop ensure you are using your GPU and not the iGPU by checking the ingame Video Settings menu. If it says anything except for the name of your GPU then you need to force the PC to use the GPU by going to your NVIDIA Control Panel/AMD Catalyst Menu and forcing the GPU.