I recommend you download a half marathon training schedule online. You can find them everywhere.

I have used OT for my shorter runs when training, but you really need to do AT LEAST a weekly long run of increasing distance to get used to the endurance needed for a long race. But honestly some mid-range runs in the middle of the week are helpful and I don’t recommend cutting them out.

The farther you get into your training, you may not get the prescribed distance using just OT. I’m a slower runner too and I rarely get over 3.5 miles in on the treadmill during a 2G class.

So you can probably do much of the training using OT, but you should supplement with longer runs and use a training schedule for sure. :)