I’ll do ~2 miles for a warm up with light stretching and a few strides.
Given that you just ran 17:15, I think you are VASTLY underestimating your half marathon potential. I’m probably in about 18:15 shape and I ran just under 1:25 two weeks ago. Also, the difference between 1:25 and 1:28 is huge. Someone in 17:15 shape should be able to “jog” a 1:28.
Can’t wait to hear how it goes. I’d bet that you’re closer to 1:22, than to 1:28.