I have ran this AP twice, and in both instances, the PCs wiped out the Lizardfolk to a man, taking almost no damage themselves. At this point, your PCs are probably extremely paranoid about the deadliness of the AP, especially after the previous module. As a result, they are tossing fireballs, buffing up reach/combat reflexes fighters with enlarge person, and other tactics for dealing with 'trash mobs', which the Lizardfolk unfortunately qualify as. Personally, I knew what was coming in the next two modules, and decided to let them have that one fight to feel awesome about themselves before the more lethal parts of the AP resume. Any semblance of tactics will dominate this fight, so don't feel bad about giving them an easy victory. There are still a couple of dicey moments in that module even (the end of it), so my advice is to let them have their moment before they get turned into Spawn of Kyuss.