Odd performance issue

I have installed sparrs mod loaded, block transform tools, block loader,. I have a issue where when i start my game, it runs at 60 FPS. But the issue is after around 10-20 minutes, the FPS is 10-5. As the game runs, it drops the FPS in a gradual decline.
You can try to find steam downloaded creations in your Steam folder (for me its that directory: 'D:\Program Files\Steam\steamapps\workshop\content'). Inside 'workshop\content' are few folders and one has many folders inside it. Some of them are empty but others has my downloaded creations inside (each one in seperate folder). Just copy .bsg files and paste them to 'SavedMachines' folder