As seen from Issue 110349, the saving mechanism of OOo is - 

1) Unreliable
2) Slow

For large files, actually the slow part is obvious, there's no work around
except by incremental saving, which's difficult to implement.

However the saving mechanism could be enhanced by splitting a large file into
many parts with a predefined nomenclature. There should be a saving mechanism by
which a document will be split to many parts after it has reached a certain size
(which will be defined by the user). All splitted files will contain info about
the size after which the file should be split, by using this and the
nomenclature of the broken files (which will be searched for) the document will
be opened as a whole.

The document will be broken from the beginning to the end, thus saving a
document will only recreate a single file rather than many or a large file.

It might happen that a user deletes certain section of the document, making one
part lighter... this will be accepted as it is. To fix this issue however
there's be an option to recompute all the parts and recreate them.