Seriously these image files sizes are getting insane. 16MB per image! If people are insistant on uploading 6000px images, then they're going to need to really focus on optimizing these images. That means using a Grayscale index, cleaning up the scan page blemishes, and using a lossy/lossless compression format (TinyPNG, WebP, JPG).
There is no justifiable reason a 25pg manga needs to cost almost half a Gigabyte