RangerDangerV2 5,000+ posts
CarAudio.com Veteran
3.5 is not large. As far as "getting away" with a smaller box, yes you can many times. However there is always something lacking. You can play low with a small enclosure as well, just not with the same type of intensity you can with a larger volume ith those drivers. The idea behind designing is to get the most from the subs in the given application. Not to "make it work".
those 15s are in less than 2.5 cu ft per sub. plays down to low 20's with ease.