Looks like a well planned out trip worked out great for you. Even better, you got a legal king. I didn't know there were any left there haha. I have only caught rats there for the last 5 or so outings.
From my experience, the more pressure you put on kings, the more they want to go straight for the bottom and bust you off and this is a problem from the rocks. So if you have small gear, don't put a heap of pressure on them or they will just bust you off in no time, instead, take your time and play the fish.
15lb is a little light, I use 50lb braid from the kayak, no point in any more for me or I would end up in the drink myself. The Chinese bloke ain't wrong saying 80lb, you will need it for the big ones. I've seen 100cm+ kings caught from the rocks on 15lb line with the fights taking over 15mins, so sure you can have some fun.
I don't remember the entrance being that deep. Maybe it is on a high tide. Right off the wall it drops to about 15m and in the middle about 20m.