I have a sorta strange problem that I really can't seam to find the answer to. In my World 1 (22.1MB) It started lagging really bad the other day. so today I just came home to play the new update, hoping it would be fine, but its just as bad. Im probably getting less than 1 fps. So I figured it was the mods that my friend told me to get, I saved only my "Saves" Folder and deleted my whole .minecraft folder, so when I restarted MineCraft, it would just rebuild the default files again. So after I did this, I replaced my "saves" folder, and boom! it still lags uncontrollably... 

So then I decided to do a quick experiment and built a World 2, Its perefectly fine, doesn't lagg at all, What the Heck??? is there some "forbidden" thing I did in the world thats causing it to lag? I made a big Waterfall inside a castle and started building a glass dome in the sky? im just super confused, I really don't wanna have to trash that world, any suggestions?

(I attached an image to what the waterfall looks like)