wow agreed everyone just goes into too much depth on the issue.Pros of 15's:
Can have a higher DB
can have higher RMS then 12's
Has bigger cone area in results in more air movement(louder)
Hits lows depending on cone area.
Produces Bigger sound waves.
Cons of 15's:
Not as accurate(refering to speed the woofer vibrates at)especially for like metal music with double bass. they are not very accurate in hitting that type of bass notes.
cant hit highs very well.
They are not very punchy. 15's are usally made for excusaions. long held out bass notes.
Pros of 12's
Very punchy.
Accurate bass
hits a wide range of notes
depending on brand they are very clear sounding
Cons of 12's
they dont hit low notes like 15's do.
pending on cone size/brand/type of sub and all the variables they are most of the time not as loud.
they dont hold up very long when they are used for excurtions.
they dont move as much air BUT!!!!!! that depends on cone size and sub tpe and brand
ALL OF ABOVE DEPENDS ON AMP,SUB BRAND,SPL SUB OR NOT,AND DB RATINGS. SO DONT ***** ABOUT HOW SOMEHTIGN COULD BE DIFFERNT DEPENDING ON THE CIRCUMSTANCES!!!BECAUSE I JUST SAID IT ALL DEPENDS ON THE VARIABLES.
hope that helps u out