Here the 1874 RLDS edition changed the past-tense had to the present-tense have. In addition, the not was changed to no. The 1908 RLDS edition restored the original had not to the RLDS text. It is quite possible that the 1874 change in tense was influenced, in part, by the present-tense usage in the following conjoined clause: “neither has God saved them”, the reading of the copytext for that edition (the original text read “neither hath God saved them”). Here in Alma 14:15, the critical text will maintain the earliest reading, “that ye had not power to save these” (and, of course, “neither hath God saved them” in the following clause).
The Book of Mormon definitely prefers the expression “to have no power” (there are 16 occurrences), as in Mosiah 23:39: “nevertheless he should have no power to do any thing contrary to the will of the king of the Lamanites”. But there is one other example of “to have not power”— namely, in Mosiah 13:7: “ye see that ye have not power to slay me”.
Summary: Maintain in Alma 14:15 the original had not (“ye had not power to save these”); also restore the biblically styled hath later on in the verse (“neither hath God saved them”).