Yeah it's 12-15 reps, but it's 3 seconds down and 1 second up, so that means each set is anywhere from 48-60 seconds before moving on to the next exercise.
You won't feel much of a burn until about rep #8, then after that, the lactic acid builds up in you and you'll be screaming (on the inside).
My max is 225 also, and I tried 135 the first time and it was rough. I had to drop it down to 95 to get through the next sets. But the first couple of times you do the circuit, you'll get a feel for what's comfortable for you.