The 1840 edition introduced the preposition of between hill and Amnihu. The RLDS textual tradition has here maintained the intrusive of. This insertion could be due to Joseph Smith’s minor editing for the 1840 edition, but there is a greater probability that the of was accidentally added by the 1840 typesetter since elsewhere in the text there has been no tendency (in any edition, much less the 1840) for of to be added or deleted in the expression “the hill (of) X”. In most cases, the text reads without the of (in 13 out of 15 cases):
The instance of “the hill of Jerusalem” is a quotation from Isaiah 10:32, which reads with the of in the King James text.
We do not have the original manuscript, only the printer’s manuscript, for the reading “the hill of Shim” in Ether 9:3, but this reading contrasts with the expected “the hill Shim”, which does occur (in Mormon 4:23). It could well be that the reading in Ether 9:3 is an error, especially since it does sound rather odd given the otherwise consistent use of “the hill X” for Book of Mormon geography.
This problem is related to the optional use of of in other expressions, especially “the land of X” versus “the land X”, which occasionally shows variation in the history of the text. See, for instance, under 1 Nephi 17:7 for the use of of in the phrase “the land (of ) Bountiful”. Similar variation can be found for the expression “the city (of ) X”; see under 1 Nephi 11:13 for discussion of the phrase “the great city (of ) Jerusalem”. Since variation is possible, the critical text will permit not only the occurrence of “the hill of Shim” in Ether 9:3 but also the lack of the of in “the hill Shim” for Mormon 4:23. Similarly, the original “the hill Amnihu” will be maintained here in Alma 2:15.
Summary: Maintain the phraseology “the hill Amnihu” in Alma 2:15; most of the time the Book of Mormon text omits the of in the expression “the hill (of ) X”.