At least you give an explanation, unlike the original Konosuba author who keeps Kazuma as the lowest level quartet member in a completely inconsistent way. In Vol 6 of the light novel, Kazuma says he is level 17, and in Vol 13 he says he is still below 20, and even a lazy bastard like him had already killed enough monsters to be above 20 by this part of the story, He even mentions that he bought several XP-rich foods, but his level didn't increase.
By the way, do you have plans to add food that gives XP to the game? Maybe have Kazuma learn cooking skills, which is light novel canon?