Use the following options:
Select the Enable Background Updates option on the Drawing tab of Application Options. This option quickly displays raster drawing views for large assemblies and calculates precise drawing views at the background as you work. You can review the drawing or create drawing annotations before calculation of drawing views finishes.
Design view representations save memory if you turn off the visibility of components that do not have to be seen. Components with visibility turned off are not loaded into memory.
Level of Detail representations suppress unneeded components or replace many parts with a single part representation to reduce memory consumption.
Click Open an Existing File , and locate and select the assembly file.