It should be noted that if the formatting stays the same that means that each background takes a page. That means there are 17 of them.
At the barest minimum, there will probably be 12. One 'Quick Build' Background for each class. So actually... here's an interesting thought-experiment: What would be the 'Quick Build' background for all 12 classes if we assume they are all different? We've already seen a bunch in previews and such, but what are the rest? My guesses:
Barbarian - Urchin
Bard - Minstrel
Cleric - Acolyte
Druid - ?
Fighter - Soldier
Monk - Folk Hero
Paladin - Noble
Ranger - Guide
Rogue - Criminal
Sorcerer - Hermit
Warlock - Charlatan
Wizard - Sage