Even if you've been lifting, I wouldn't skip the 15s. You should be taking the full SD (in your case, seeing as you already lift, 12-14 days). After the SD, the 15s really help to prep the connective tissue and protect against injury, plus, you'd be quite surprised how many of us have experienced gains on the 15s!
That said, assuming that you do skip the 15s, you could do as you suggest- four weeks of 10s and four of 5s. If you do, I would set up your progression scheme so that the last week or two of each would be at the appropriate max. That will avoid the problem of insufficient load during the first week or two at each rep level. So, here's one scheme (assuming 3x/week):
10s:
M: 50% 10RM
W: 60%
F: 70%
M: 80%
W: 90%
F: 100%
Next 2 weeks: 100% 10RM
5s: as above, just based on your 5RM. Also, I'm assuming that you're not doing negs, but if you are, then I'd do tose the last two weeks of 5s, per the HST plan.