People commonly talk in terms of how many ships are on a single team, not in terms of how many ships exist in the match.
A "6 Cruiser match" would be in reference to having 6 Cruisers on each side. Saying there was a "12 Cruiser match" would be considered odd as that sounds like either Tier 1 or an all Cruiser match (meaning 24 total).
The term you probably want to use is a "double CV" match. That implies 2 CVs on each team.