Yes, compression refers to how much space can be saved by "loss of variety of information", basically. More compression means more grouping together of tones or colours close to each other as one colour. Less compression preserves more of the original. When you "save as" a .JPG file, Corel Photo-paint will call up a dialogue box where you choose a compression factor and (in later versions) a smoothing factor (which "smoothes out" some of the artifacts that can appear during JPEG compression, those little specks and spots with sort-of haloes around them you'll often see in very compressed JPEG images).

To save further space, convert the black & white ones (not the sepiatone ones though) to 8-bit greyscale palette first. No need to waste space used by a 24 bit colour palette on greyscale images that only used the first few "colours" (which are really shades of grey). No picture quality will be lost by converting to the smaller palette and they will take up much less space and be easier on your computer memory too.