vaping a 1.5Ω dual-coil atty is like
vaping two 3.0Ω atties at the same time. Yes, you get more vapor, but that vapor is cool, unless you crank up the voltage way up--and hope that your battery can supply the amps. You're draining the battery (your battery still reads the 1.5Ω resistance of the atomizer) and using up the
juice at double the normal rate--for not much reward.
That said, many people like dual coils and the extra vapor they provide. Others like the warmth of the top-coil design--since the top coil (both in dual coils and in top-coil single coils) is placed so close to the vaper's mouth, the vapor feels warmer.
Electrically speaking, we're dealing with a parallel circuit--1.5Ω dual coil is really two 3.0Ω coils side-by-side on the same connector. So the voltage must be calculated for 3.0Ω, NOT the 1.5Ω. Which means, if you like 6 watts of power, you'll have set your voltage to 4.2v if you want to achieve that wattage with your DC 1.5Ω device.
It's complicated.
As always, YMMV.