Again, some people fail to include important details.....
How much space are you talking about for each setup? Ported? Sealed? Box facing which way? What vehicle? Too many factors to say for sure which would be louder but one thing is for sure..... IT'S ON IN THE INSTALL!
The set up is going in a 1971 Impala the trunk measures L X W X H: 61 X 25 X 16. All the subs will face the rear of the trunk. I more than likely will go with a sealed box.
Cone Area Wise The 15's Displace More Air But Its That Compared 2 Four 12's..so U Really Not Going To Hear A Difference......but 8 10's Yeah U Will Hear A Difference.....but As Said Earlier.....it Depends On The Install