The guide is based on my personal experience playing Space Architect.
These advices may or may not help you.
But I wish I knew them earlier.

You may also experience low FPS because of the hardware.
These advices will likely help you if you have similar hardware or better.

My PC spec:
Laptop, Acer Aspire 7
i7-7700HQ
GTX1060
16GB RAM
M2 SSD 512 GB
Windows 10

I assume you've read description and disclaimer.

So you've been playing for 3-5 hours straight and experience low FPS.
These actions helped me improving FPS from 10-20 FPS to 100-150 FPS.

1. Save game
2. Exit to the main menu
3. Load save


It is as simple as it is.
Maybe because it is likely a one developer person game, it lacks certain optimizations.
But still I enjoy it and want to help others enjoy the game too.