Thanks to the both of you for your answers again :)
I have the reading on Instruments (xcode).
So, i made mesurements. I use a single eventsheet for all the project and i thought that maybe the pb could come from here, cause all the layouts are by consequence connected to it.
I made 4 exports to test :
1 - eventsheet present and 14 more layouts duplicated : 49 MB.
2 - eventsheet present and i got rid of the 14 : 42 MB.
3 - eventsheet deleted and 14 more layouts duplicated : 45 MB.
4 - eventsheet deleted and i got rid of the 14 : 36 MB.
i've not touch at all to the textures.
I don't really know how to read that cause it's not very logical.
Event if there is a pb with my eventsheet (i will search, but i don't know if the ram can be changed by that), it doesn't explain the big difference i have when this eventsheet is not in the project, between the built with 14 more layouts duplicated and the other one.
I still have a huge loss of ram (9 mb).
I'm too tired tonight to continue (lol), i maybe miss something somewhere. A good night and I will have fresher ideas on it :)