In Europe, Celts, HRE, and Netherlands start very close to each other. Why not just choose one of them? The same applies for Byzantium and Ottomans who start in exactly the same location. It used to be Constantinople - Now it's Instanbul! Also the Babylonians and Sumerians start very close to each other.
Would it be possible to mix and match a few of them so that you have about 14 to 18 civs on Earth and they have some room for the AI to function?
EDIT: I am adding what I think an appropriate mix for 18 civs will be:
Americas: Choose 3/5 Civs (Inc, Az, Maya, NA, USA)
Africa: Choose 3/5 Civs (Egypt, Mali, Eth, Car, Zulu)
Europe: Choose 4/12 Civs (Eng, Net, Fra, Cel, Ger, HRE, Rus, Vik, Spa, Por, Grk, Rome)
Middle East: Choose 4/6 Civs (Ara, Per, Otto, Bab, Sum, Byz)
Asia: Choose 4/6 Civs (Mon, Chi, Ind, Jap, Khm, Kor)