His rights were violated, of course he is going to sue; that's normal behavior. According to him, he wasn't allowed to contact his parents when he was being questioned / arrested. That's illegal.
The $15 million figure is mostly due to the nuances of the American justice system. It's a purposefully inflated figure that his lawyers likely came up with. People rarely get the full amount they ask for, but lawyers always ask for more than they expect to get in the hopes that the deciding judge will use that figure as a baseline. It's the same reason why mass murderers are often charged with multiple types of homicide per victim.
The $15 million figure is mostly due to the nuances of the American justice system. It's a purposefully inflated figure that his lawyers likely came up with. People rarely get the full amount they ask for, but lawyers always ask for more than they expect to get in the hopes that the deciding judge will use that figure as a baseline. It's the same reason why mass murderers are often charged with multiple types of homicide per victim.