Deleting all Ztables and using only ZQuerys I can decrease all the memory consume up to 41Mb.
If you use Absolute Database, the same code and the same database structure and data, it only consume up to 17Mb, including 6 ABSTables opened with MasterSource option betwen them.
Probably it's zeoslib that reserves more memory than needed for the data in the tables. It reserves the full capacity of string fields (eg 255 bytes for varchar(255)). So if you have a lot of big string fields which you rarely complete completely you'll see that much waste. You could also try to create forward only readonly datasets. These might waste less cache memory as they don't need an update cache.