Hey this is for anyone with the Island Paradise lag who doesn't want to use mods to fix it.
I had this problem only in the IP world, where the sims and edge scrolling and cursor would freeze but everything else carried on as normal.
After a bit of research I found a few things that stopped the lagging and dramatically improved load times :)
To fix the lag: delete all houseboats and houseboat lots, and go into every lived in house in the world, changing things that would get NPCs stuck, or things that don't work. e.g inaccessible bathtubs and furniture too close to get around. (you should be able to create your own houseboats without the lag happening if you build it with plenty of room to move around)
This is in your Sims 3 folder on your computer...
To speed up your loading times: delete these cache files (they will reappear, but this is incase one was faulty) simCompositorCache.package, CASPartCache.package, compositor Cache.
Delete all images in the Featured Items folder, and deny access to it to stop EA adding more useless images there.
Delete everything in the DCBackup folder, except the ccmerged.package file.
