The problem with an afk kick is what if someone is legitimately afk and the rest of the party is fine with it. The main negative way a vote kick can be abused is kicking people after they've already contributed to the group, so I'd just set it up so the vote kick can only be initiated within the first 10 minutes. Sure you could be vote kicked out after the first boss of AK but the chances of getting past wall within 10 minutes are incredibly low.

So what'll happen is a group will wipe on psychflayer, blame someone for it, kick them and try again with someone new. With the current system the group wipes on psyche, someone gets blamed, that person gets belligerent and refuses to continue but is quite content at just afking until people leave. Someone then decides to leave, that person gets the 15 min debuff, the other two most likely also leave as well and the last person, the one that threw the hissyfit gets to then try the fight again with no penalty with a new group.