Hi Mark thank you very much for your detailed feedback and for playing the game!
Performance on my Macbook Pro 2013 wasn't good either while in Unity but was quite okay when playing the build. On what kind of system did you try to play it? We have most of our textures already on low quality because of that. + Thanks for the bug report!
PS: We added an WebGL version to itch.io which runs much smoother now if you want to give it another try with better performance.