As far as I know, it isn't possible to only install certain items from a world. It's all or nothing. You haven't mentioned your system specs either.
This is a comprehensive write up - https://www.nraas.net/community/TIPS-FOR-BETTER-GAME-PERFORMANCE
Be discerning with your custom content. Don't simply download just for the sake of it. Ask yourself whether you really need it, or if something from the game or an EP might suffice. I try to keep my CC folder at 3 gigs or under, because of performance. Sometimes broken or badly made CC can cause slowdown in your game. Try to stick to creators that are known for making good quality CC, and always read the comments or reviews before downloading to see if anyone has experienced any issues with the content. Usually, if there are three or more people who have all experienced the same problem, I either download warily and test for myself, or skip it.
TS3 will reward you tenfold with wonderful gameplay if you take care of it, but it does require a lot of kid glove handling to make it run nicely.
This mod here - http://modthesims.info/d/478307/remove-stencils-overlays-from-build-buy-cas-objects-in-game-edited-01-16-2014.html has been a godsend in my game. It has reduced my need for custom content simply by being able to remove stupid stencils or ugly overlays ( and speculars ) that EA have put on some game items that would be nice if not for ugly additions. No more cloth jackets that look like shiny leather, or pretty shirts with horrid stencils on them.
Check to make sure that you don't accidentally have any Sims 2 packages mixed up with your Sims 3 packages if you play TS2. Those will slow your game down immensely due to the games inability to read them. You can also follow the steps here - http://simswiki.info/wiki.php%3Ftitle%3DGame_Help:Package_File_Lag Using Process Monitor can help identify problem files. I still check this way sometimes, and it helped me find some blinds, which were a bit of a problem in my game. Once I took them out, it was good.
Clear your caches , etc, the usual. I also delete my world caches after every second or so play session. Not everyone does this, but its part of my TS3 voodoo ritual :D My game runs nicely so I keep up with it.
Other than that, I've never played the game using Origin, and would never, so I'm afraid I can't help you with the Fast Lane thing, except that I've seen people say the game / Origin unticks EP's or SP's by itself and that you should probably check that horrible Origin isn't deciding for you which SP's you should be playing with.
Someone more qualified than me can probably determine if your hardware is a bit underpowered or something, if you post the specs.
