kalanne from Nigeria for a 15hrs 40mins layover at xiamen international airline

Kalanne, if Xiamen is your only stop within mainland China and if the cities immediately before and after Xiamen are in different countries, then you are eligible for 24 hour visa free transit and you don't need any kind of visa. For example, if your itinerary is:

Seoul - Xiamen - Bangkok

Tokyo - Xiamen - Hong Kong

Then you are fine for 24 hour visa free transit.

You will print out your flight tickets and have those printouts with you. Since your layover is a long one, you can try to obtain a temporary entry permit by applying at 24 hour visa free transit counter, upon your landing in Xiamen.