April 08, 2013, 2:59 PM — Here's how you can change the Speaking Rate in Speak Selection on your iPad, iPhone or iPad.
1. Go to Settings.
2. Go to General.
3. Tap on Accessibility.
3. Tap on Speak Selection.
4. Adjust the Speaking Rate by using the slider. Left makes it slower, and right makes it faster.
For more, see the original article at the link below.