Dear AllanUK,
During the 15rep phase, I try to do giant sets with minimal rest between sets. This means I'd do all my sets for chest at once, then do all my sets for back, then leg etc. The reason for this is to get as great a pump as possible, but more importantly, as great a metabolite buildup as possible. Thus, during the 15s, the burn is of essence.
When it comes to 10s, I'd rest long enough to catch my breath. This could be a minute or two. 10s are perhaps, the transition between 15s and 5s, and with good form and a minute's rest or two I keep the burn there but at bay.
When it comes to 5s and beyond, I have ample rest between sets. No more than five minutes though. I think Ruhl had made a posting on rest times and ATP regeneration and someone else had gave guidelines on rest between sets. The post is "Why Do Conventional Sets?". Try that post and see.
Godspeed, and happy HSTing
