The original manuscript is not extant for the word out here in Alma 58:15, but spacing between extant fragments indicates that out was probably in 𝓞. In the printer’s manuscript, Oliver Cowdery initially wrote “to come against us to battle”; but then virtually immediately he inserted the out supralinearly (there is no change in the level of ink flow). The original text probably had the out, just as it does earlier in this verse: “except they should come out to battle against us”.
There are six other occurrences in the text of “come out … to battle”. On the other hand, there are 14 occurrences in the earliest attested text where no adverbial element such as out, up, or down appears in this expression. In fact, one of these examples appears nearby in this chapter: “nevertheless we could not come to battle with them” (Alma 58:6). So either reading, with or without the out, is theoretically possible here in Alma 58:15.
In general, we have the following statistics in the original text for adverbs of location in the expression “come ... to battle”:
Since there is considerable variation with respect to choice of an adverbial in this expression, we let the earliest textual sources determine the correct reading for each case, thus out here in Alma 58:15.
Summary: Accept the reading with out in Alma 58:15 (“to come out against us to battle”), the corrected reading in 𝓟.