Writer is running very slowly.

I’m using Writer for uni work but it’s running terribly slowly. Even scrolling up and down through the text is laggy. Typing is also slow and painful, as it takes some time for the words to appear.

I don’t know what’s causing it. I’ve tried increasing the memory used in the options but it hasn’t helped. The larger the document the worse the slowdown gets. Any ideas on how to improve performance? I’m running Windows 10 64-bit on this PC at the moment.