when its a big party of 15 what does it mean that we will only get a "chefs menu"does that mean ?

There is a pre-set menu that guests can select from. There are different price points to allow you to have a wider variety of items

it's apre set menu created by the master chef

You get a pre-fixe menu of certain items the guest cam choose from. There are different levels of pre-fixe you can choose, more expensive usually means more choice or more high end selections.

A pre set menu created by the chef