References faster than base / original file ?

My case:

I want to ask because i have to render 60 flats on 5 floors in same position but in near top perspective .

I need a flats in same position but the flats have other shapes and clip volumes. So i'm not moving Camera but moving file to marked / clip point

As i see - moving whole design  with interiors  is so slow and sometimes crash  but  i found solution  - new file and design as a reference. Now i can move it faster and render.

Why references are faster in this case ? If they have same elements / same info  ?  Maybe because can't be edited - so are smaller / faster ?

Martin