There is no minimum speed limit. However, the faster you type, the better is student experience due to less waiting time.
If you don't type sufficiently fast enough, you can type the lesson and assessments before the session and just copy-paste during the session. Using a whiteboard with a digital pen also bypasses the need to type fast as you can draw directly on the screen.
Given that most of us will spend a big chunk of our lives typing, it makes sense to learn to type fast. The proper way to type is to touch-type i.e. typing without looking at the keyboard. It took me about one month, one hour per day, to learn to type at pro speeds. I used typing master software. Now you can use typing software like Typingbolt.