10-30 seconds sounds very slow indeed. It used to be slow for me (over 10 seconds against my university server), but I discovered it was because I had not deleted emails and propogated that to the server, I had only marked them for deletion (d), not deleted (D), and so there was some kind of syncing back and forth each time of quite many emails with mbsync. For me now it is always under 5 seconds for syncing and indexing, usually quicker.
You should read the book by Barbara Minto named "The Minto Pyramid Principle: Logic in Writing, Thinking and Problem Solving." See http://www.barbaraminto.com/textbook.html