The EGA version was 4 1.44MB disks for MS-DOS, IIRC. Let's say 5MB. That's about 30 disk sides or 15 disks in DD disks. Not that bad actually, and perhaps the C64 images are smaller or more compressible than the EGA ones... So this should be some kind of an upper limit.

It has to be less if they don't want to spoil the in-game 'insert disk 144' joke ;)