I did about 10 15 second strides because I felt do good! I did do some walking in between, only about 15 seconds , then I would jog and then sprint.
I usually do (roughly) 100 meter strides. I end a lot of my runs on the sidewalk of a road that has nice straightaways & a lot of street lights. The lights are roughly 50 meters apart, so I sprint 2 lights, and then slow jog 2 lights, repeat. When they're written into my training plans, they're usually anywhere from 5-8 sets. I think I've gone up to 10 at the end of a mid-week semi-long run, but I rarely do that many. Sometimes I just throw them in when I'm bored. Last week, I randomly threw 4 in at the end of a 7 miler.