Maruf You say 'weight' - but is it the actual 'size' of the resultant SKP file or the 'heaviness' == 'slowness' in editing or navigating around the SKP etc after the import ? Have you also kept the CAD files 'origin' [see import > options], if so then that can slow the SKP; also sometimes CAD 'Blocks' become SKP 'Components' with strangely placed origins, you can change the component's axes to somewhere more sensible by using the right-click context-menu... Have you used the SKP's Model Info > Statistics > Purge Unused after the CAD import as there can also be a lot of unneeded stuff brought in even after you've purged the CAD version first. Also run 'audit' on the CAD file after a 'purge' just to ensure there's nothing wrong with the CAD data before the import...