Why can't I add more HTML-codes on my funnel before it becomes laggy?

I’ve used a few HTML-Codes from a different website, and it works fine to use parts of it, but not more than around 2K rows in the HTML-sections before it becomes laggy. I want to add more parts, but it just won’t let me edit them further after pressing save. The lag makes it impossible to edit. Anyone know what to do?