I forgot to mention , it is the first thing I did
Of course I have increase memory to 4Go. This doesn't change anything and I notice, the amount of memory used is not very different between paramater in plist.info set to 1GB or 4GB.
I didn't notice other parameters I could tweak ?
Regarding object I can set transparency to 0: Does this concern all object of the whole project ? For instance : If I render the ground, I should disable of object which belong to First floor ?
Juju