It may be because your world is too large for your computer to handle, and with full graphics on, any unanchored parts may cause lag. Removing it or anchoring it should solve the problem.
Well here comes the first problem- This world is practically nothing compared to some other games iv made. And they handle unanchored parts pretty easily
I just find it weird that it does this. As the game is currently only around 10k parts
Were on other games might have up to 20-30k parts and seats nor unanchored objects affect gameplay