SE 3rd Gen has 4GiB RAM, therefore the app defaults to 384x384 size. This is about 1/2 computation of your normal run (512x512) and the original version uses PLMS sampler, which defaults to 50 steps, while this one uses the newer DPM++ 2M Karras sampler, that defaults to 30 steps. All in all, your M1 Pro MBP is still 4x of your SE 3rd Gen in raw performance (although my implementation should be faster than PyTorch at about 2x on M1 chips)