Is it possible to merge map tiles?

Hi everybody, is it possible to generate in Maperitive tiles of different areas and with the same zoom level(ie 15) and then merge the 15 folders toghether, overwriting the folders with the same name to obtain an extended map tiles formed by the previous map tiles?
If not, is there a way to create tiles of a large area, proceeding in multiple steps?
I ask this because i have to generate tiles of a very large area that goes from the Gibraltar chanel to Greece, but i have only 4 GB of ram and Maperitive works only in ram and if i try to load all the .osm files(i already downloaded) my pc blocks completely and windows reboots.
Thanks in advance!

Hi SamaritanMan,

for questions about maperative it would better to ask!forum/maperitive

In general: maperative works at the moment only with OSM-data loaded in RAM from a local file (OSM or PBF). For an larger area you would need an postgis-DB (e.g. postgres) with osm-data and an renderer (e.g. mapnik), which supports postgis-DBs as an data source. This scenario works with linux and in rare cases (only for experts) with windows.

This is a little bit more complicated than maperative, but nearly all big osm maps works like this.