The previous chapter ended with Nephi’s testimony, punctuated with amen. In both Nephi’s and Mormon’s writings, when the word amen appears as a testament to something that has been written, or quoted, it ends a chapter. There are a couple of exceptions where an amen does not end a chapter, but, in most of the exceptions, the amen is simply recorded as the end of a prayer, and not as a separate testimony.
This literary technique begins with Nephi, but is consistent throughout what we know of Nephite writings, since Mormon uses that same technique almost a thousand years later. What is most interesting is that the testificatory amen closes a chapter even when the story is not finished. This will create the condition where the end of the story is appended to the beginning of the next chapter, rather than stay in the same chapter as the rest of the story, which is how a modern writer would do it.
In the first verse of our Chapter 15, we see the result of closing the previous chapter with amen. That forced the end of the chapter, but Nephi wanted to signal that that part of the story had also ended. Thus, he notes that after the vision, he returned to the tent of his father. Nephi continues to use the tent of his father as a marker for the change of stories. This has happened within chapters up to this point, but it occurs at this point as well. In this case, we have just this sentence before picking up the new story. Nephi, as a writer, closed the previous chapter with the testificatory amen, but closes that story with returning to the tent of his father.