Cropping on Premiere Pro - help!

Hello, I am using the crop tool with keyframes to animate cutting out bits of a painting (see attached)

However as i add more crop effects, premiere pro is slowing down to such a rate that it's impossible to work. 

Because i want the crop to be cumulative, I have to keep adding a new effect everytime, which is why i think it's slowing down. Is there any way i can do this in premiere or is it something that i should do in After Effects, and if so does anyone have a good guide?

Also on a side note, the speed has suddenly dropped. It was working well for quite a while. I have nested quite a few times. I am using proxies, a SSD, the media cache files are on the SSD inside the computer, while the files are on the SSD external drive. I am using OpenCL renderer. Is there a way it could be because of something else?

Any help would be massively appreciated!