Slow loading can be cause by many things as you might have read it in the documentation.
1. What does the average request runtime on the performance tracker submenu? (Performance tracker)
If it's below 3-4 seconds, then something else is clogging up the ajax request.
2. What type of hosting do you use? Shared or VPS? What are the server specifications?
3. How many plugins do you have activated? Plugins count greatly descrease the ajax performance globally.
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