RE: H.I.I.T question / interval training ?
What your doing sounds less intense than HIIT.
HIIT would be more like this.
4 mins light warm up
15 secs flat out sprint
45 secs very light jog (almost walking pace)
Start out at 5 sets of this, or more if you can, then try and add more sets over time.
You cant do proper HIIT on a tradmill - too dangerous.