Kicker atleast need 5 cu.ft internal volume in ported box,to put out what it is maintained for.....!
And About Type R,than wrong theory Jz......Type R 12" can pick lows and loud frequencies equally good,If put in a proper tuned ported box...!
Type R 15" can also do that and go more into loud and low due to bigger in size....!
Your 15" Type R giving you lows because previously you are using it in sealed enclosure and after that you put it in 30hz ported enclosure....So you expecting to play loud frequencies from it...??