Wolfenstein

Edit: This no longer works in a private match!

Easily boostable with 2 people.
Set up a Stopwatch match on Rooftops, have you be Resistance and your friend Axis, or vice versa.

Once the match begins, complete all the secondary objectives on the way to your first primary. Once the ramp is complete, run to the next secondary objective and quickly build it. Ignore the dynamite plant below, and focus on running to the primary objective and quickly deliver it. That's 2 Primary and 4 secondary objectives in 3 minutes or so.

Have your buddy do the same when you switch sides.
You should be in the speed veil whenever possible, and equip the "quick hands" perk so that you complete objectives quicker.

Doing this will net you and your friend the achievement in less than an hour and a half.

Note: You can also obtain the "run-gineer" achievement while doing this, or be very close to getting it when you are finished. Just stay in the speed veil whenever you can.

I just want to add some information to the solution by NarrBitaYarr.

You need 30 primary any 50 secondary objectives. Rooftops earns you 2 primary objectives every time, which means, you have to play 15 matches of Stopwatch.

Besides the 2 primary objectives you can get up to 5 secondary objectives. 1 of them is the dynamite mentioned above. You should skip this all the time. If you do the maths, you'll see that you'll get 60 secondarys if you do all 4 every time. So thats 10 too much. You can save some time if you do 4 secondarys in the first 5 matches and then only do 3 in the last ten matches. When you start out, build the machine gun (1st secondary). Then run ahead and plant the dynamite at the sniper-tower (2nd secondary). Run 90° to the right and you can build a protection wall (3rd secondary). Run around the wall and build the bridge (1st primary). Run over the bridge, turn left and run up the slope and turn right again. Run ahead, down the slope and turn left. Run straight and you end up in a wide open area, where you can build another wall (4th secondary). A little bit to the right and straight ahead would be the dynamite which you should avoid, so instead run to the left and straight ahead, till you can enter the generater area to the right. Cross this area and enter the building where you can pick up the intel (2nd primary) Exit the building again and run across the generator area and further straight ahead, till you come to a ladder. Climb it up, enter the building and you can transmit the intel. I'd suggest skipping the first buildable wall after the first 5 matches, since it blocks your path to the bridge when it's built.

I stopwatched a match and with the annoying loading, waiting and warmup times, one 2player-match of 2 rounds (i.e. every one does the objectives once) takes about 8 minutes. Take this times 15 and you end up with 120 minutes. Add meeting and loading times to that and you'll see, that you need a 2 and 1/2 hour session for this achievement. It took each of us only about 75 to 80 seconds to finish a round. So you see, that you spend more time waiting than playing when you do this.

Edit: to profit from "Quick hands" you have to activate your veil-speed while building, which uses up energy, you could also use for running faster. So I don't know, if it's worth trading in running speed for faster building. I guess it won't make any difference timewise.

By the time you have done 10 runs of Rooftops, you will have about 50 secondary objectives and 20 primary objectives, so you'll only need primaries.

On the map "Hospital" there's a little trick you can do with the first primary. How it goes is that the first primary consists of two doors, with you needing to blow up one normally, but if you plant dynamite on both and let them finish before you finish the final objective, you now have 3 primary objectives under your belt.

Doing this is much faster than doing "Rooftops" for primary objectives and should take at max 3 minutes per run. Like the other solutions, you should have quickhands on to speed up doing the objective.

Found this out when we were in the middle exp boosting and objective boosting and picked the wrong map.

If you negative vote this solution, please leave a comment and I will see how I can improve.