Yes, Taming The Flames is incredibly difficult, even at level 15, I found out the hard way.
Ammassing pots and fire-protecting items for it is a "must-have".
If you know how the quest works it's not so difficult. The main thing is to avoid fighting all those fire elementals. The summoned ones don't move and respawn. So it's a waste of time attacking those. You just run fast past all the spawning points of the summoned elementals.
If you have a toon with evasion it's much easier to complete the quest. DDoor helps a lot too.
The quest is horrible if you don't know exactly what to do. Then you get killed moving around trying to figure out what's next.
It's actually easier to solo Taming the Flames than being in a group. Partly because of monster scaling, but also because you then control completely which monsters will spawn etc.
Most of the times we've wiped on this quest it's been because some players (I won't mention our party member who truly dislikes Super Mario parts of a quest
) move into the big room with traps and lots of fire elementals and then fall down and get killed. That means the player with evasion who got the key has to get the soul stones of all the dead and in the process die too from the crossfire.
You handle the big room by flying directly down to the chest. Open the lock and then ddoor out if you can. A scroll of ddoor is the rogue's best friend here. All others stay away from the room and wait for the rogue to come back to them.
If you have plenty of past lives and reaper points then you can even survive all the fire damage. Especially on a tiefling sorcerer.
I wouldn't recommend Taming The Flames to a first lifer, though.