Which would sound better?

i have two 15" l7's in a box i built @ 34 hertz in a 12cf ported box but even though i have bass cd's none really accomidate my set up so my 15 rarley ever do much because it s set for subsonic only basically and i was wondering would it be better to switch to a smaller box or tune it higher so as to get more of the 12" sound because these things should be rocking. i got a 2100 amp on em