>>2024898Your file is huge because the scan interacted with the screentones to cover everything in Moire patterns.
Little localized black & white checkerboards, if you look closely. PNG is lossless, so it saves all of the unnecessary (really, unwanted) detail.
I Gaussian blurred it 0.8 pixels and the file shrank to 1.8 MEG. Converting it to grayscale reduced it even more.