<div></div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">I just sometimes feel like I get no results from the 15s or the 5s</div>
If you were to do HIT you would soon find out what making no gains is all about. You would initially get a bit stronger because you would be training to failure and thus stimulating your body to get better at making a max effort (there's a proper scientific reason in the FAQs). However, if you were to do squats and deads to failure three times a week you would probably start coming down with coughs and colds on a frequent basis (I did). Then you'd hit a plateau and soon get depressed that your progress had ground to a halt despite your best efforts. My advise would be not to bother but give it a shot if you want to prove it to yourself.
As Faz says, 15s will probably not give you much in the way of size gains (although so far I have managed to gain a pound or so during 15s and get a really good pump going) but they do prep you really well for the heavier stuff. If you leave them out you may start to get joint/tendon issues here and there.
Feeling like you aren't getting results is not the same as actually not getting results. What do the scales, mirror and tape say?
You should be able to make gains during the 5s and post-5s if your routine is sound and you are eating right, but it's a good idea to do some higher rep metabolic work too. Have you tried doing that?
You can always post your routine, poundages, diet info, bf % etc. and I'm sure we can all pool our collective thoughts to get you gaining again.