We experienced the long time taken by Experience Editor to load which in turn frustrated the Content Authors so I will share the fixes we used to make the experience editor load faster.

There are 2 things we can do but for that your website and client should be okay with it: 1. Hide or Stop loading the Header and Footer in Experience Editor because it is common for all pages and are very rarely updated.

2. Disable automatic testing if you are not using A/B testing in your site.

Note: Once again Ill reiterate myself, to do above fixes you should check with your customer and implement.

To implement the point 1. We can just wrap the html structure of Header and Footer with a if statement checking if it is not Experience Editor:

@if (!Sitecore.Context.PageMode.IsExperienceEditor)
{
@Html.Sitecore().Placeholder(“header”)
}

To implement the Point 2, you should be sure that A/B testing is not used in your website.

1. Go to your website instance folder.
2. Go to App_Config >> Sitecore >> ContentTesting folder.
3. Open the Sitecore.ContentTesting.config in Notepad++.
4. Change the value of the setting “ContentTesting.AutomaticContentTesting.Enabled” to false.
   

These two points should fix the issue of slow loading of the Experience Editor.

Thank you.. Keep Learning.. Keep Sitecoring.. 🙂