I got the answer why the lagging is serious while styling objects in buy mode. I took out all store items from DCCache folder, then the lag is gone without store items... I need to cut down the amount. 3.43 GBs of store items is too much for the game I confirmed.
https://www.youtube.com/watch?v=M3Y8sMVuGdo
You can see it's almost impossible to style ONE wallpaper at 1:30. I tried to put the palette on the right wallpaper but it didn't let me do and pused it to the ground. The pattern loading speed is incredible but styling is horrible without buydebug cheat on. I was having 121 mbs of userpreset file in the sims 3 folder, and I tested this after throwing it away. There's no any saved patterns or anything.
