That does sound pretty likely. Would take up ~64 MB of video RAM. My machine has 128Mb and can run this at a pretty decent speed, but if you have 64MB or less this code is bound to run into speed issues.
(What happens if you force a 16 bit video mode? Wouldn't that cut the memory requirements in half as well?)
(What happens if you force a 16 bit video mode? Wouldn't that cut the memory requirements in half as well?)