Text editor lags when editing long post

One of my posts is very long. Lately, when I edit it, the text editor lags. A second or longer passes between when I hit the key and when it appears on the screen. This makes it difficult to work with.

I looked up similar problems and found the advice to disable emojis, but the problem persisted even after I installed the Disable Emojis plugin.

This is the page in question: https://www.samanthalienhard.com/2015/10/screenshot-lets-play-tales-of-zestiria.html

What should I do?