Going about it all wrong if thats your frequency response goals. 2 12s in a ported enclosure tuned to 28-30hz will outperform your idea of 2 15s sealed.
09 sienna B pillar 6th order with 4 team ascendant 18s on two taramps 15ks
320 amp singer alt, 6 group 31 agms in the back (battery revamp in the works)
80 prs, 3 way front with head unit + amp crossovers, massive ct 2 german silk tweets, pwx 10s in the doors, PRVs 6mr500 ndy in the kick on ct 500.2 to the pwx 10s, ppi 900.4 bridged to prvs, ppi 600.2 to the tweeters.