IP is unfortunately known for its lagging, there are a few suggestions (sourced from here, credit to Crin) that you can try:
- Delete the Scott Family (premade, lives on a house boat) from your game
- Use the cheat DiscoverAllUnchartedIslands to make all Islands visible. I am aware that this takes away from the world but it has helped a lot of people
- Make sure you don’t have any stuck Sims (use resetsim * to reset all your Sims and animals)
- Search the ocean for abandoned boats and delete them through testingcheatsenabled true –> Shift-Klick an the boat –> Object-Delete
- Routing Issues in the Resort Hobart’s Hideout
You can also take a look at these:
If none of those helps, you can still save your family and move them to another town
- go to edit town
- click on your household and choose "save to library"
- exit to main menu and start a new world
- Move in your sims from the library
You'll lose all your relationships if you do that, but it's better than nothing
