Island Paradise and Into the Future are somewhat demanding, not as much as Pets or Seasons but enough to impact performance. Stuff packs shouldn't have any effect. The impact of the expansions should be limited to lower framerates, if anything, unless you're playing in Isla Paradiso or another broken world. Lag shouldn't be an issue in normal circumstances, at least not on your hardware—it's usually a sign of something in-game taking all the resources, for example a stuck sim that the game engine is continuously trying and failing to reroute.

You don't necessarily need to uninstall to see a difference though. I'm not sure what kind of install you have, but if it includes Katy Perry, it sounds like you're not using Steam. For an Origin install, you can deactivate packs in the launcher; for a disc install, this tool is useful:

https://modthesims.info/d/499140

Keep in mind that if you remove an expansion from an already existing save, you could corrupt the save or the sims in it. Removing a stuff pack shouldn't matter, other than the "items removed" message you'll get.