Here in the printer’s manuscript, Oliver Cowdery initially wrote be healed as believe. Almost immediately, he crossed out the lieve part of the word believe and supralinearly inserted healed (there is no change in the level of ink flow). Oliver’s error was undoubtedly influenced by the occurrence of believest in the preceding clause (“if thou believest in the redemption of Christ”). A similar misreading involving be healed is found later on in the text; in this case, an original behold was misread as be healed, an incorrect reading that has persisted in the text:
Once more we see the influence of a preceding verb form, in this case be healed. For further discussion, see under Alma 33:21.
Summary: Maintain in Alma 15:8 Oliver Cowdery’s corrected reading in 𝓟: “thou canst be healed”.