Exercise will temporarily lower your bp, but then it comes back up again. What I don't understand is why if your readings average around 115/75 to 120/80 you were told to INCREASE your dosage! Unless you have some medical condition that requires much lower blood pressure, 115/75 to 120/80 is considered normal with no further reduction needed. On top of that, your doctor told you increasing your dosage wouldn't lower your bp very much anyway - so why is he increasing it?
You need to seriously quiz your doctor on his rationale for your increased dosage. If he can't give you a good answer, insist you go back to 160 mg. There is no reason to take more medication than you need to keep your bp in the "normal" range.