d15z6 d15z8 is basically y8 head with vtec-e valvetrain, so yes you can swap head internals and have *real* vtech (if you were asking about this),
and yes 190cc is still enough,
iirc the intake lift/duration of d15z6 cam is close to d16z6 one,
but you'll need to tune it, 'cause vtec will not operate properly with vtec-e ecu.
on the other hand, it will start and even run )