Here the 1830 typesetter accidentally changed thee to you. But everywhere else in this passage (verses 15–17), the angel uses only the thou /thee /thy pronoun forms, never the ye /you /your ones:
A similar example of the exclusive use of the thou /thee /thy pronoun forms is found in Mosiah 3:3–4 (see the discussion under Mosiah 3:3). Both here and in Mosiah 3:3–4, an angel is speaking (here to Alma, in Mosiah 3:3–4 to king Benjamin). The critical text will maintain the systematic use of the second person singular pronoun forms in both passages.
Summary: Restore in Alma 8:15 the thee pronoun since in the larger passage (Alma 8:15–17) the angel addresses Alma with only the thou /thee /thy pronoun forms.