At the end of chapter 15, Bilbo is grumpy and tired and wishes he were anywhere else.
Bilbo is upset because the adventure is not going well. He is tired of the trip. He is homesick. Thorin has refused to give him any of the treasure, since he is not family (though Bilbo did have a contract). No one was brave enough to contradict Thorin, and Bilbo decided “disapproved of the whole turn of affairs” and had had enough of the mountain.
"The whole place still stinks of dragon," he grumbled to himself, "and it makes me sick. And cram is beginning simply to stick in my throat." (ch 15)
At this point, adventure is losing its luster. Adventure is actually full of danger, disappointment, and frustration. With Gandalf not there to intervene on Bilbo's behalf, he feels outnumbered. Also, he feels as though they are stuck between a rock and a hard place.
Despite Bilbo's bad mood in this chapter, he sticks with it. In general, Bilbo proves himself to have the right stuff. No matter what danger or discomfort is thrown at him, he comes through.