Isaiah 13:15 (King James Bible) every one that is found shall be thrust through and every one that is joined unto them shall fall by the sword
At first glance, it appears that the Book of Mormon’s proud might simply be a visual misreading of the King James found. The original manuscript is not extant here, so this is a distinct possibility. However, the parallelism of the whole passage suggests that the original Book of Mormon text read proud. Note how the King James Isaiah text places no restriction on who will be slain (“every one that is found ... every one that is joined unto them”), but the Book of Mormon text restricts it to evil people (“every one that is proud … every one that is joined to the wicked”). This parallelism strongly supports the Book of Mormon reading.
Alison Coutts also points out (personal communication) that a previous verse in this chapter supports the association of proud and wicked here in verse 15:
Summary: Accept in 2 Nephi 23:15 the reading of the earliest textual source, proud; although visually similar to found, the word proud is most probably the intended reading because the phrase “to the wicked” replaces the italicized King James unto them in the following parallel clause.