The file size as saved bears no relation to the ultimate size of the 3D file.
For instance, you could have a project with 10,000 3D trees in it, but saved as a project file it is one tree called 10,000 times. To render that file, your computer must "build" the model, making vertexes and polygons of the GDL script. This, and the various lighting, transparency and shadow calculations during a render are what makes huge RAM demands on the computer.
But, most of the time, "memory full" is caused by a corrupted element and you need to methodically isolate the element to remove or repair it.
Dwight Atkinson