If Trump gets 15 percent of the black vote then that means Biden gets 85 percent or a 70 percent margin. That’s a lot better than GW Bush’s 8 and 11 percent, respectively. So if one million black votes are recorded in GA, this means that Biden’s margin is 700,000 rather than the 840,000 that a Bush eight percent share for Trump would indicate.
In Georgia Trump will get a much higher % of the black vote than nationally because southern blacks are more conservative. Herscell Walker like. There is some evidence from North Carolina that Republican and Unaffiliated black men are over performing in VBM.