I found it depends on how I maintain the game. These are some factors that slow down on performance:
- large/old cache files (some of them should be deleted occasionally)
- lots of CC/mods
- a big screenshots folder (and probably video folder)
- many households/houses etc saved to my local gallery
- many saves
- a large population with a long backstory
- CC files with filename including special characters (ie []''%& space) (affects loading in BB mode negatively)
- many items in personal inventories and household inventories
Adding:
- Limited free space on your main drive + minimum computer specs.
- Many other programs running in the background (probably affect performance more than loading, though)
