Forget pain. That's end result. Avoiding the mofo that's actively trying to kill you is what makes you feel much alive.
Just need to add in. The 15-20 min wasn't a one shot deal. They nail you with it for 15-20 min let you go to whatever detail you were on (raking leaves was a pain even if there were no leaves which leaves you nice NC sand dirt which gets rake to). Then they haul you back in for another go. The OHDarkThirty shake down is a mind nuts kick. At this point your really screwed because your body craving sleep, your mind craving sleep, your body ready to to go shut down but nnnoooooo ice cold water on a hot body will jolt every fiber of your being back into reality and the "
WTH am I doing this again?" hits your mind. Then the "pain" goes into effect. They are allowed to hurt you and at times they can break small bones. I signed the waiver
Also in SERE school you cannot opt out. You sign the waiver, you picked the
MOS, you volunteer to certain types of units and you know the effect of opting out in a
DA school. You do not quit because in SERE school if you quit then your more likely to give up on life if your in the real deal. Also if your really burned out by "quitting" they stick you in the sweat box. Not enough room to lay out nor stand up. but its peaceful for 4-6 hours.
edit
You are aware 110% before going in on what's going to happen. I've never been slapped around so much in my childhood as to what I got myself into but at times I wanted to curl up in my piss poor of an excuse of blanket suck on my thumb and cry while gently rocking myself back and forth