Unfortunently, no. 15 is the maximum number of chairs that are able to be added to a single appointment book.
The only option is to create another appointment book with the additional chairs on it, or a mix of what is most efficient at that point.
Sigh....that's not an option for us. We have 4 doctors with 2 columns, one with 3, one with 1 (soon to be 2) and 5 hygienists. We need to see ALL chairs at all times when scheduling.