Do you have checked bags...? I agree that 15:20 would be taking a chance but if you don't have bags then your odds get somewhat better. Also, what is your incoming airline... if its a SkyTeam member then maybe you can get check through boarding passes...? AR is part of SkyTeam so this may be of some use, depending on which airline you are coming in with...?

Not advocating you take chances, just trying to help you reason though your options and plan accordingly. And I do agree with malagajohn that there is quite some "random" component in the entire customs/immigration processing time.