I'm suffering the same symptoms you are -- but ONLY with non editing teacher roles.
Student and Admin are blazing fast. NET's take 5 seconds to load.
I'm going to guess your on Moodle 3? There look to be some big time performance issues.
You might try upgrading to the newest Moodle and see if that helps. We can't upgrade at the moment. I wonder if this will help you.
Did you discover anything else since your original post?