I've done HST with a similar rep max. Here's what I did (rough estimate):
During the 15s - 2 sets x 4 reps, 2x5, 2x6, 2x7, 2x8, 2x10
During the 10s - 2 sets x 7 w/ 5 pounds, 2x7 with 7.5 lbs, 2x7 w/ 10 lbs, 2x7 w/ 12.5, 2x7 w/ 15, 2x7 w/ 17.5
During the 5x: 2x3 w/ 20lbs, 2x3 w/ 22.5, 2x3 w/ 25, 2x3 w/ 27.5, 2x3 w/ 30
Obviously I wasn't following the basic template, but I was slowly increasing the weights. If the weights felt really heavy, I repeated the weight for the next workout (that's probably not following HST to a T though).
This was a while ago, but one of my friends tapped out with 4 reps for chins. I had him do something like this:
During the 15s: two sets of 1 rep (great form); two sets of 2; first set 2, second set 3; two sets of 3; two sets of 3; first set 3, second set 4
By the 10s, he could do more reps, but the progression was still slow.
Hope that helps.