Going from 23 to 20 will be a pretty large jump. My suggestion is to find someone who regularly runs that fast and run with them, or a person on a bike, or with a dog.
I suspect you are right, it's definitely going to take some work. A 6.66 mile (ha Bellavite where are ya?) is what I need, and I can do 1 mile in 6.66, but 3 is another story.