How much should I level in the Stories Demo?

So far my party consists of:

Blue Kut-Ku: 17

Velocidrome: 15

Azuros: 13

Kut-Ku: 10

Aptonoth: 16

Have I overleveled? I really don't want to not use my monsters but I don't want the game to be too easy later on. Should I stop here or os the game going to get way more difficult?