Well, if there are things you want to save... like if a door has been unlocked or locations of moved items, or something along those lines, you could make them Global items or give your objects the Persistent behaviour.
As for the memory issue. Think of the Alphabet. Currently you need to load A, B, C, D, E, all the way to Z. But, if you make smaller layouts, as I suggested, you only need to load A, B and C. Then when you go to another layout you load E, F, G and so on.
I know it might sound a little confusing, but if your target device is mobile, then this will really help in the performance area and the sooner you use this method the less work you will have later in development.