Scan Tailor if you want to split them. Maybe you can try outputting a lower DPI than 600... (with a DPI
calculator, perhaps?). If you wana use it on comic books, set it to grayscale. In colour they would just take up more space - especially if you're reading it on the current E-Ink technology (which is monochrome).
If lowering the DPI doesn't work, Irfanview can also batch resize.