Why is 15,16-dihydropyrene aromatic?
While doing calculations for Huckel's rule, in polycyclic compound only peripheral pi electrons are considered for aromaticity.
So, 7 double bonds in the periphery i.e. 14 pi electrons.
14=4(3)+2
Huckel's rule satisfied. Aromaticity achieved.
Why are only peripheral pi electrons considered?
The reason is that only these elections are participating in delocalization for conjugation. If multiple bonds occur in the centre like in pyrene these central bonds will not be localized. Thus, only peripheral pi electrons are considered in conjugation.

Therefore, first 2 compounds in this image are aromatic and last one is weakly Anti aromatic or Non aromatic.
We can't commit compound to be aromatic on ONLY Huckels rule with this compound must be

Cyclic
Planar
Complete cyclic conjuction
Huckel's rule

Here in 3rd compound,
Due to crowding of Interior Hydrogen compound loses its planer nature. Thus, not called to be Aromatic.
(I have attached 3d structure of cyclotetradeca-1,3,5,7,9,11,13-heptaene (3rd compound)
Please refer it.)