Designed a Buck converter, Need to add galvanic isolation
I can think of a reason why this inductor is not suitable: the core. This is a common-mode choke, designed for EMI suppression, not energy storage.  The 6 amp rating is for differential-mode current, that is, current flowing through one winding and returning through the other.  Since the currents are equal and in opposite directions, the resulting MMFs cancel and (neglecting leakage inductance) there is no net flux produced. So the current rating is more a function of resistive losses than core saturation. 

Most common-mode chokes are wound on a high permeability ungapped ferrite core.  Using only one winding, the core will saturate at far less than the 6 amp rating, even less than your 0.6 amp maximum.  

Even if you operate below saturation, the inductor will likely be noisy at 15kHz because high permeability ferrites have a magnetostriction behavior. Also, ferrites for EMI suppression have high losses at higher (200+ kHz) frequencies.  Switching at 15kHz, you have harmonics in this range, degrading efficiency.  

By the way, because both windings are on the same core, connecting the windings in parallel (assuming the MMFs are in the same direction) is like using a heavier wire.  Compared to a single winding, the dc resistance will be half, but the inductance will be the same.