Here the first printing of the 1852 LDS edition read in the plural: “the words of his commands”. (The tilde in word ~s means that the s was set upside down.) For the second printing of this edition, this plural s was removed, probably by reference to the 1840 edition. All other textual sources have the singular word here in Jacob 2:15.
As discussed under 1 Nephi 16:24, the Book of Mormon text often uses the singular word to refer to the word of God; thus the use of the singular word is fully acceptable here in Jacob 2:15. For a similar example of this kind of variation, see the discussion under Jacob 2:11.
The text has a similar example of this particular expression “the word of his command(s)”; in this case the singular command is found rather than the plural commands:
Despite the difference in command(s), this other passage does have the singular word, so there is therefore nothing inappropriate about the reading “the word of his commands” in Jacob 2:15.
Summary: Maintain the singular word in Jacob 2:15 (“and O that ye would listen unto the word of his commands”), the reading of the earliest textual sources.