Hey I had also been in your shoes when I was practising controlling rate of speech. I have realised that body gets habitual of how do you speak whether it’s slow or fast or with slow rate of motion. For example if your follow speaking slow, After some time you will notice that you can easily switch between normal speaking and your slow rate according to the situations. At the end what matters is how clearly you can communicate with the the other person no matter how it sounds in starting phase.