I also am playing on my old laptop.1. As my pc is currently in repair, ive been playing on my old laptop.. i notice the game has performance mode... but i dont see anything different with it.. the main thing causing lag imo is the lightrays overlay, and the clouds/leaves flying across the screen.. if performance mode could disable that, it would help a lot.
For me version 0.5.6.6a is just all around slow. I couldn't handle it and went back to 0.5.5.0, it plays quick even with the leaves flying across the screen. Not using performance mode either.
I hope there will be an option going forward of not using all the new graphic animations during regular gameplay, when things slow down like this it makes a game unplayable for me.