I would change the know reputation to be a knowledge based roll, with the DC being [Arbitary number, perhaps 13]-[Reputation]+/-[Other Modifiers...].

For average joe that's still a int based check, but it makes more sense in my mind than a DC 15 check that means level 6's 'might' be heard of by average joe. Especially given that by level 6 your supposed to be epic. With 13 and the above, by level 6 theres a 50/50 average joe has heard something about you.