If you are having issues with slow loading of tickets, or the reply editor template loads with a delay, you might need to change the amount of quoted text that you include in your answers.
A solution to both of these issues is changing the number of how many recent messages are quoted. This can be configured in Configuration > Email > Customer templates separately for each template type and department.
The reason for the slow loading is that even though the quoted text is not displayed anywhere, it is loaded into the browser and is ready to be inserted in the editor when you click the button at the bottom of the reply editor Edit quoted text.
Unless you are legally obliged to quote the entire communication history, we recommend quoting only the last 1 or 2 messages and adding a link to view the whole ticket in the customer portal in a similar way to how we add the link at the end of our replies (see image below).