Do not fret. Heavy is whatever is heavy for you. Ignore whatever anyone else is lifting. Cathe says in her intro spiel that when you first start out you may even have to lower your weight to begin with until you get used to the extra demands that the slow count makes upon your muscles. If you take the momentum out of the move, it is purely muscle that lifts that weight. It is fabulously challenging. After a 2 week period, you will find yourself hitting your stride and wondering to yourself, "hmm, perhaps I could do 15's for chest rather than stick with the 12's as usual." So, you try it out and discover that yes, you can do it and you are suddenly lifting more than you ever have before.
It does not matter if your usual weight for chest presses is 10 pounds in each hand. You will make progress. If you go up from 10's to 12's or even to 15's, you are making as much percentage progress as someone who goes up from her 15's to a new weight of 17 per arm.
No matter what your level, everyone can make use of this series.
Clare