Whole Software Is Laggy... (Read post for more details)

So I am currently making a palm tree and used and copy and pasted about 10 or so PNG leaves. I think this is what is making normal actions so laggy, and I'm not sure what to do to make it Un-Laggy. I converted it to a symbol and that didn't seem to do much. So now I'm stuck on what to do to un-laggify it XD... so if you have any suggestions, plz let me know thx!!