According to the impressions a Hebrew language expert had while reading the Book of Mormon, verse 15 is very significant:
The sacrifice in the altar and Lehi dwelling in a tent suggests that he could have been celebrating the feast of tabernacles. This feast is also associated with bearing fruit - see Lv. 23:34-40. The main theme of this feast is that we give up our comfort and rely upon G-d for our sustenance. This matches the theme of the Hebrew in this chapter.
It is also important to notice that this feast happens in a period of time when it's fall in Jerusalem and is about the time when it starts to rain heavily.
Also consider the fact that this was a feast in which there were pilgrims coming to Jerusalem. Nobody would normally flee Jerusalem at this time. By leaving Jerusalem at this time Lehi was making a very bold statement that the Shehinah-Presence of G-d was no longer dwelling in the holy city.
This shows the boldness of Lehi: Fleeing Jerusalem right before the great feast and taking his odds in a journey during the pouring of heavy rains. This explains why those who had not been touched by the Spirit of G-d would have thought him to be out of his mind.