Oldspook, here are the things that I did that helped with the lagging the most for me in the town of Isla Paradiso. They make IP playable for stretches, but eventually that little stuttering gets under my nerves. Lol.
4. Overwatch mod from Twallan. It resets stuck sims and cleans up a lot of other "file junk" that tends to accumulate. But I have had to have it running since the Late Night EP.
5. Register mod, also from Twallan. I use it to completely turn off all the stray animals, wild animals etc. This world seems to have a lot of pathing bugs, and places for sims to get stuck. Being able to turn off 20 or so animal sims that always kinda bugged me in the game anyway eases the number that can potentially get stuck.
6. In edit town, I kicked all the townies out of their houseboats, moved them into other empty houses, and then got rid of the houseboats as well except for those that my active household owns. This one cut down on a lot of the lag/stuttering.
7. I cleaned up a lot of the lots that were built with bad pathing practices. Like a section in the Spanish styled resort's pool. There is a fenced in area in the middle of the pool, but still had something inside that fence that NPCs like to "view". The game in this situation, has probably thousands of potential tries to get to the object inside with routes over the pool, but the fence negates the path each time. Yet the game's pathing engine is going to run through all the options every time an NPC thinks he needs to check out that object. Another situation in houses, were circular stairs with walls placed in ways that often make them unusable. I replaced these with ladders most times or moved the blocking walls/objects. The castle looking house, where the Ichtaca family lives, had a number of situations. Once I cleaned them up, Overwatch stopped telling me they were resetting one of the family members ten times a day or so. Another area was objects in closed in areas that were only accessible by the garage door style of doors. These don't auto-open for sims, and for some reason NPCs can't open them in their pathing either, so again the game potentially has to try to figure out all the potential options before it gives up. I noticed this mostly in the modern resort lot. The VIP rooms have little outdoor deck areas that are not accessible any other way.
8. I got rid of the Scott family. Several people on the TS3 forums have said they were saved in the town in the middle of an activity and that object isn't there anymore. Or something like that. Those with the Error Trap mod, say it goes nuts over this family. So they had to go from my game.
For a few people on the EA forums and others that I read, one of the above steps completely cured their lag, so they might be worth checking out. Isla Paradiso really is a beautiful EA world.
For me doing the above items (I simply deleted the ones that didn't apply or I didn't do) turned IP into a playing paradise.
Overwatch is a must have mod. If you have no other mods you should still be running this.
Register is new to me. I always just turned off pets in the options, but being able to completely turn off all strays, just doing this cut my lag down to a third of what it was prior. Says to me that a lot of the lag is the spawning wildlife.
I was surprised as well that moving the townies out of houseboats cut down on the lag. It's unfortunate I suppose but really as long as my sims can be in a boat I don't really care all that much about the others. I might not do this step though next time I play, just to keep the flavor of the town going. As I said, using register alone cut down dramatically on the lag.
The fenced in pool was a definite problem and an easy fix...thanks for spotting that.
The stairs and the Ichtaca family catches were also great and easy fixes. edit: nope still had problems after all, ended up deleting the house and putting a new house in there and it is fine now
Removed all the garage style doors when I found them. No noticeable improvement but possibly because it was only a small problem and I had already fixed the bigger problems from before. edit: wasn't garage doors I removed after all, was something called zebra doors...not the ones you mentioned I don't think, so I went through and changed all doors on all VIP rooms.
Deleted the Scott family and again, a very noticeable improvement. Something definitely seemed wrong with them.
Thanks so much for this info, using just the steps above has given me a nearly lag free experience in IP. Basically the only lag now is at 3am when overwatch does a brief clean up, and even then I almost never notice it the lag is so short.