I wouldn't have a problem with giving the players a really tough fight (especially since this would happen when they have no time pressure), but I wouldn't want to just wipe them out with a hopeless fight. In 5e I haven't played much at higher levels or Dmed yet, so I don't have a good feel for how these things work, so I might just be underestimating just how much higher level characters can dish out. The first Module is for levels 5-7, and the 'typical' 5e party size is 3-5, and a purple worm is a CR15 monster, which makes it seem like this a TPK waiting to happen to me.
Most of the conversion makes sense to me, but one thing that seemed odd is that they did a straight 'use the 5e monster stats' for purple worm encounters.
I recently picked up 5e conversion PDFs for the classic Desert of Desolation modules.
