The earliest extant text for Alma 54:15 (namely, the printer’s manuscript) has a pronominal repetition of the subject Ammoron (namely, “Ammoron … he was angry”). The original manuscript is not extant here; spacing between extant fragments is sufficiently long that it is difficult to determine whether the redundant pronoun he was in 𝓞 or not. But the he is definitely in 𝓟.
The editors for the 1920 LDS edition removed the redundant he since its use here in written English is nonstandard. But the original text had numerous examples of such redundant usage, some of which have been edited out of the text. For some discussion and examples, see under Mosiah 8:7 and Alma 43:36. For a general discussion, see under subject repetition in volume 3. The critical text will restore all instances of this kind of redundancy, as here in Alma 54:15.
Summary: Restore in Alma 54:15 the redundant subject pronoun he, the reading of the earliest extant sources (in this case, 𝓟).