Vault 15

Vault 15 was one of the Vaults built by Vault-Tec. It was supposed to stay closed for 50 years as part of the Enclave's Vaults experiments. It was also overcrowded. It contained occupants of diverse ideologies and ways of life, a situation that led to the schism, during which 4 groups of people left the Vault, three of which later became the Jackals, Vipers and Khans raiders, and the other one created the Shady Sands village. The three first decided to harass the fourth, and each-other, for dominance.

Quotes
Vault 15 - "Unfortunately, we were crowded and life was very bad. There was a schism, and many people left, taking with them the best equipment.  Still, some of us tried to stay in the Vault.  But then we were attacked.  I was hurt, and I ended up here.  Now I try to help people..." - Katrina of Shady Sands

Appearances in games
Vault 15 appears in Fallout and Fallout 2.

Inconsistency
The layout of Vault 15 is vastly different in the two games.