So your average PC walks 30 feet a round (or 60 with dash). In the module, there are two environmental hazards back to back.
The first one 2d6 (7) damage a round and 100 feet to escape. There is a Dex save for half, which most PCs will have a 30% chance of making. So the PCs can make it out, with maybe 7 points of damage if they run.
The second one 2d6 (7) damage a round and 300 feet to escape. Same Dex save. So 4-5 rounds to make it out depending on their initiative. So 28-35 points of damage to a level 4 character - DEAD!!!!
Heck, how about a 1st level tagging along? Sorry about your luck dude.
I think that the damage and the Save DC are too high for the level of the players. I think we will have several TPKS or character deaths.
I know that there are a couple of solutions, turtle shields (if they all have them), horses go faster, but your average PC on foot is going to die.
P.S. Who is the old friend in the blurb?
5E players probably didn't play Crusade.