During 15th century, slaves were common in pagan lands, not so much in christian europe anymore.
Prisoners of war, if they were unimportant enough to get ransom for, were still kept as slaves here and there, and taking prisoners (say, sons of a noble or warlord) was a brutal way of keeping peace: you attack us, we’ll slit your sons throat first. In feudalism, heir is everything! Often, peace was made on condition that surrendering party gives his heir as prisoner (to make sure they’d keep their word and plot no revenge, but also to control, influence and weaken them).
This was needed because there was no modern border guard and early warning systems: an attack meant several villages got looted and burned before noble even found out that his lands are being attacked. So it was easier to make sure there’s no attacks at all, instead of defending and weakening both your army and economy. Also, peasants getting raided might get quite rebellious against their lord who didn’t protect them…
Slavery was more “okay” if slave was not a christian. But slave could sometimes ask to convert and get protection from the church. For captured women, converting, turning to church and asking to become a nun was often a way out of being a forced wife for a warlord or noble that captured them. Catholic Church was higher than everything but kings (and even then somewhat).
As for races, only highly controversial possible thing in time and era would be high anti-semitism and gypsy hate that roamed everywhere and is still timeless. I’d imagine Warhorse Studios simply avoided this issue for good taste.
There were little to none africans in those lands I’d imagine, and if there were any, they were probably treasured merchants or advisers or envoys. Definitely not slaves or something looked down upon. Although curiosity people might have towards them would be called quite racist today.
Male prostitutes and whatnot is science fiction. While obviously some existed, such radical rarities have no place in this game. Church was also the moral police and even if some noble or knight had fun with his servant or page, this happened in utmost secrecy and mouths were filled with gold to keep them shut.