[Origin Version] UI Missing in Strangetown + Intense Lagging in Tokyosou

Sims 3 has been Large-Address Aware since 2010 and can therefore use up to ~3.7 GB RAM, as in, 4 GB minus some overhead. If the save is using less than 2 GB when you first load it, then that's obviously not the issue. And 1.5 GB memory use is perfectly reasonable for a new save that uses most or all expansions.

Do you have all the expansions installed that these worlds use? Is there any other recommended content that comes with the worlds and that you don't have installed?