In these two passages, we see some early confusion over whether the verb form should be hath or has. In the first example (verse 15), the hath variant is firm since the corrected reading in the printer’s manuscript agrees with the 1830 reading (for this part of the text the 1830 edition is a firsthand copy of 𝓞). In the second example (verse 16), the printer’s manuscript originally had hath, but the 1830 edition had has. In his editing for the 1837 edition, Joseph Smith corrected 𝓟 so that it would agree with the 1830 reading (just as he did in verse 15 when he emended return to turn in accord with the 1830 reading). But in the 1837 edition itself, Joseph’s emendation to has in 𝓟 was ignored, probably because the text expects the more biblically sounding hath when referring to the Father’s commandments, especially given the archaic inverted word order with thus (“thus hath the Father commanded me”). The modern form has would sound more acceptable if the passage had the normal noninverted word order (“thus the Father has commanded me”). See under Mosiah 12:1 for further discussion regarding the use of hath as the biblical style in the Book of Mormon text.
Summary: Maintain in 3 Nephi 16:15–16 the two readings with hath; this form is found in the earliest extant text for this passage; moreover, this is the form expected in the biblically styled language appropriate to this passage.