Here the 1858 Wright edition omitted the repeated definite article the. The first two RLDS editions followed this shortened reading, but the 1908 RLDS edition restored the repeated the. Elsewhere in the text, when the nouns heaven(s) and earth are conjoined as noun phrases, if heaven(s) takes the definite article the, then the the is repeated for earth:
Here in Alma 1:15 the noun phrases are conjoined within a prepositional phrase headed by between (of course, the between is not repeated). The other examples of the conjoined heaven(s) and earth serve as either a subject or a direct object noun phrase, not the object of a preposition. Yet in all these cases, the the is repeated. Thus the original reading in Alma 1:15 is the consistent reading and will be retained in the critical text since it is also the reading of the earliest textual sources. See the general discussion under conjunctive repetition in volume 3.
Summary: Maintain the repeated the in Alma 1:15 (“between the heavens and the earth”).