I have not seen a definitive limit, but there may be problems for people viewing the page if it is very large. A message I see when creating cemetery pages is "some browsers may have problems with this page" when it starts to grow large.
It would be preferable to break up large amounts of information for various reasons. For instance, someone on limited bandwidth may have problems loading such a large amount of data, especially if they have to do it at multiple sittings.
Systems with limited resources may also choke.
Perhaps converting the memoirs into one or more downloadable pdf's (uploaded as an image) might be a better option, and the free space page used for a summary.