Yes, and moreover:
If ∀a∈A∃b∈B[b≤a], then every lower bound of B is a lower bound of A. Thus, infB (if exists) is a lower bound of A. Thus, if also infA exists, then infB≤infA.
No need to assume that the two are comparable. Boris (talk) 08:02, 17 April 2016 (UTC)