Panzer Leader (which was way simpler than JTCS, it was a card board game after all) stated any towed artillery.
Or maybe there was a caliber mentioned? Too lazy to pick up the rules book although I have it stacked here somewhere...
We could of course intepret it to be after a certain caliber.
We still had some original Russian 76K/36 guns when I was in the army in mid 80s believe or not, and while they were not heavy as such it took a while to manhaul it around, especially as you had dug the chassis into ground...
In 6 minutes, maybe not? At least not for two salvos as JTCS inteprets them.
So maybe a 50% action point usage for calibers less than 80mm, and full 100% for bigger'uns?