I'm going to assume that contact was extremely scarce, and those Africans actually living in Korea was even more rare. I don't know under what conditions the contact would have been typically but for the "average" Africans that were in Korea at this time looking to integrate, how did society treat them? How was life ..if at all different?
What? Africans?
In 15th century Korea, there were
Jurchens: After all, Sejong's grandfather had Jurchen ties
Japanese: Mostly traders and former pirates, concentrated on three southeastern ports
Probably Chinese, who had a constant presence in Korea throughout the Goryeo Dynasty
Possibly Mongols and Uyghurs, as remnants of the Yuan presence in Korea only a few decades before
Perhaps even Vietnamese and other Southeast Asians.
There were even Muslims; Sejong decreed that since Koreans disliked Muslims apparently out of xenophobia, Muslims should no longer wear Islamic robes nor practice Islamic rituals. However, these Muslims were not black Africans; they were probably Arabs, Persians, or Uyghurs.
The first entry (two "black men" are mentioned in 1395, but these may be Southeast Asians) in the Annals of the Joseon Dynasty concerning a black African man is in May 1598, when a black man is recorded to have been shown to King Seonjo. The Chinese seems to have told the Korean court that black people could breathe underwater and destroy enemy ships from the bottom. The Korean court apparently believed this, so Koreans probably had very little, if any, prior contact with black Africans.
Sources:
The Annals of the Joseon Dynasty are highly recommended if you can read Classical Chinese or Korean. Korean translation; Chinese original.
I used a Korean book about Islam in general for the Muslim presence in Korea in the 15th century, written by a professor in the University of Beijing. ISBN: 9788936470777