I used a combination of Dibbs93 and Pedle Zelnip solutions: used a second profile and just ran through the start of a new game.
I have a second profile (PlayerTwo) created on my console specifically for games like this: ones that don't allow a "guest" account to allow you to earn a co-op achievement. I loaded that up and started a brand new game.
The first 13 quests are doled out one at a time, so you'll likely get them in this order:
- Fresh Off The Bus
- The Doctor Is In
- Claptrap Rescue
- Skags At The Gate
- Fix'er Upper
- Blinding Nine-Toes
- Nine-Toes: Meet T.K. Baha
- Nine-Toes: T.K.'s Food
- Got Grenade?
- Nine-Toes: Take Him Down
- Nine-Toes: Time To Collect
- Job Hunting
- T.K. Has More Work
T.K. will then give you two quests, both of which are fairly challenging if you're around the level I was (Lvl 5-6):
- T.K.'s Life and Limb
- By The Seeds Of Your Pants
As you leave T.K.'s house, Scooter gives you another simple quest:
Accomplishing that will give you 14 completed quests and another challenging one:
- Bone Head's Theft
Proceed to Skag Gully toward either of T.K.'s quests and just after you enter the zone and pass the vending machines (before you go under the stone archway), there's a glowing, green recorder on the left signifying another quest:
- Why Are They Here?
This is fairy straight forward but you have to kill a lot of skags … but you'll have to do that for any of the quests in this area. The quest requires you to collect two recordings and, once you complete that, you can turn it in at the Fyrestone Bounty Board for your 15th achievement.
To make this even faster, I left my second character just hanging around Zed (quickly in reach of the vending machine for grenades, or either Zed or the Bounty Board for turning quests in); in Skag Gully I left the second character just inside the zone so I could easily leave back to the Arid Badlands. The character was never attacked in either of these locations.
Immediately after turning in Why Are They Here at the Bounty Board, the achievement popped for both accounts.