Cool thanks for the reply @brybro27 ... funnily enough , first thing I did after I posted was to go check that out haha. Probably should have did that first before I posted :).

For each airdrop, there will be a minimum amount required to get a guaranteed airdrop
The amount required is announced before airdrop is dropped
Amount changes per airdrop and what rarity the card is
Legendaries require a higher amount, epics require less

The above part added a bit of confusion. Especially the line about the amount changes per airdrop.

Anyways , the question now is : if one buys 750 packs , which should equal 15 promo cards ... do you get 15 copies of the first promo card or are you getting all 15 promo cards?

I would assume it's the latter , but hey ... ya never know ...