For 15 to 20 minutes of work, that’s definitely worth it. It’s just a matter of getting in the right server.
A succesful encounter shouldn’t be conditioned by being on one server or other. It should be flexible enough to be manageable on all servers.
I actually find more people migrating towards Jormag now. That was (and still is) an obnoxious fight between the different stages of it, but the new Tequatl encounter has managed to surpass it and now I genuinely see a lot more people doing that fight at all hours than those I see interested in even bothering to go to Tequatl anymore. Achievements are good to keep people motivated, but there won’t be enough people around soon for others to keep on trying. After the event is over I doubt anyone will go there anymore, just like others have already said. It’s annoyingly hard to accomplish even during the event, while meeting the manpower requirements for this fight.
I already gave up on getting the achievements, as much as I like collecting them, I’ve done my 6h of sitting, waiting for spawn, failing several times despite doing my best (it takes collective effort after all), to know it simply takes the fun out of gaming. And when a game fails to accomplish its purpose, you know something’s wrong.