Typically on a 14 night cruise there are 4 formal, 4 informal and 6 casual evenings.
As your cruise is 15 nights with 4 sea days and 7 ports of call I would suspect that the extra night would be casual.
Breakaway - 28 Apr ’17 - 9nts
New York : Royal Naval Dockyard overnights (Bermuda) : New York
Now from €1959pp
Click here to see offer
Royal Princess - 27 May ’17 - 7nts
Barcelona : Cartagena (Spain) : Gibraltar (Great Britain) : Marseille (France) : Genoa (Italy) : Florence (Italy) : Barcelona
Now from €1199pp
Summit - 27 May ’17 - 8nts
Cape Liberty (Bayonne) : King’s Wharf overnights (Bermuda) : Cape Liberty
Now from €2699pp