A lot of people are having lagging problems with the Island Paradise Expansion. This is what fixed it for me. There is a pesky Family which appears to be causing the issue. Load the game in and then find the “SCOTT” Family. Move them out and delete them. Zoom the map out and check that you can move around the map without lagging, then zoom in and do the same. Then Save the game. Thats what fixed the lagging for me !! Get rid of the Scott Family from the game !!
After that you can also try resetting any Sims that may be “Stuck” on the map somewhere while you are in game by using CTRL+SHIFT+C keys. A small rectangular box will appear Top Left of svreen then type “resetsim” and Enter.
Hope this helps
Some people have found that removing the Scott family fixes a lot of the lag. Others have found that removing two houses (Amigos and the Medina family; move the families into other houses) does the trick. Removing all houseboats and docks is another (especially with Pets; houseboats and horses is bad juju).
EllaCharmed fixed a lot of the routing issues in Isla Paradiso. Some were idiotic object placements like toilets and showers blocking each other, but others were a lot more complicated. Her fixed world can be found here:
I’ve also read that removing the fog (“testingcheatsenabled true” and then “discoverallunchartedislands”) can help.
Face it, Isla Paradiso is just a very poorly designed world. The rest of the EP is decent enough, but that world is enough to drive anyone batty.