Fifteen seems to be quite aggressive, yelling at Nine and Six when they arrive to her home. When Nine and Six pose as Fifteen, they are greeted very excitedly by the other numbers (which they speculate as the reason for Fifteen's isolation).

Fifteen also has some violent tendencies, as shown in Thanks for 2,000,000 Subscribers, She beats up Nine when they returned to get their sunglasses back & using a flamethrower on Nine when they attempted to retrieve their sunglasses again and on Fourteen (