Uhhhhh
Please don't. It's not fun. Not at all.
For 1 the majority of systems deal with intense dissociation which can be incredibly disabling on it's own. There's also the possibility of having headmates who hurt you or the body. For traumagenic systems (or even just systems with trauma) we have flashbacks. Traumatic memories can bleed through on accident.
Not to mention that we fight with each other. You trap 14 people in one body for 15 years and there's gonna be some heated arguments.
To be honest, I'm really starting to get upset with singlets who say they want to be a system because you really don't. It's not a game, it's mental health. /lu