Vayne PD + DD

No.

12% less damage taken from the target you auto-attack last, and 15% of the damage after that effect (if applicable) and after resistances is dealt to you over the next 3 seconds as true damage.

Phantom Dancer and what else? Sorry, I don't get you.

First, that would be 25.2% reduction, not 27%. Second, DD does not reduce the damage taken.