Here the 1841 British edition omitted the subject pronoun he in the conjoined clause. The subsequent LDS edition (1849) restored it. The critical text will, of course, maintain the he. See under Ether 11:9 for a list of other cases here in the latter part of the book of Ether where such a conjoined subject he has been omitted.
Summary: Maintain in Ether 15:2 the subject pronoun he in the conjoined clause “and he began to sorrow in his heart” (the reading of the earliest textual sources).