Definitely practice answers, say it twice in your head before you say it out loud or record it to see where you can slow down or improve, and keep listening to it and record it again and compare the two audio clips. I would recommend telling them you have a speech impairment, it’s not really the best if they think you’re very nervous, and I’m sure this is a situation they have faced before with past / present students. Just let them know before you start that you sometimes face difficulties reading out loud, but it doesn’t hinder your work ethic :). Best of luck with your interview, try not to worry too much. Practice makes perfect. It’s better to be over prepared rather then underprepared