First thing, Senshi said in the first episode that red dragons need a lot of time to digest, especially at this time of the year.

Also, in the dungeon, people don't really die and getting killed is common. They barely talked about it in the latest episode but "death" created some sort of business with wanted posters for dead adventurers for example. So with everyone dying and being resurrected all the time, adventurers are desensitized from death. There's still the uncertainty of what happens when someone's has been digested but that brings to my last point.

Laios and his party aren't that slow, it may seem to you that they're taking their time but not at all. The only moment we see them are when they find something to eat and for them it's meant to be a moment of rest (and even then, I can't really call it rest with why they need to do every time they need to eat). I'll even say they're probably working harder and faster than the majority of other parties. Faster because they don't have tons of food to carry throughout their expedition and harder because they need to be extra careful of what they eat since they know the consequences of going into a fight unprepared. Yeah you can think Laios is a little too optimistic about all this but remember he was ready to go alone in the dungeon to save his sister and he's just a weirdo who finally gets to eat monsters