It is reasonable to expect him to follow your instructions, but not necessarily that he can control it on his own. It is good to set the expectation of behavior right before you go somewhere as well. Learning at this age is a repetitive process. In the next few months, you'll likely notice a shift where he can process and remember instructions the first time you give them...then he'll know the rules and just ignore them...lol.
I might add though, this is a good time to set some sort of limit about how many times you will remind him in a single sitting. At that age I would give my daughter three reminders and then we'd leave the building/situation for a few minutes until she could follow directions. Now I make sure she tells me why we left so I am sure she understands.
Don't stop going out, but be courteous to those around you and be prepared to interrupt/cut your time short if necessary.