This level is a bit longer than some of the others, and if you're playing on Assassin (or playing the Assassin trick, see the solution for Treadstone Assassin), this one can be a bit annoying. This solution is primarily for those of you trying to get through the timed sniper run at the end of the level.
First thing's first. If you're going for the passports while on Assassin, you may want to consider just beating this level and coming back on Trainee. The time limit plus the snipers will make this challenging.
You have 4 minutes to make it through the end from the last checkpoint. The goal is the stairs at the far end. If you can sprint up the stairs, you win, regardless of who is still alive. Cover is essential. As you build adrenaline, hold onto it until points where it'll be the most useful.
At the beginning, you're crouched behind cover at the back end of an alley. There's one guy on the right (A), one up on a balcony (B), and one shooting from around the left corner (C). I would recommend immediately moving up to the next bit of cover, while still behind the left corner.
If you do that fast enough, once you're in cover you should have time to kill A with a headshot. Focus on him first. If you take too long, it's ok; he'll move around the middle and crouch at the top of the stairs behind C. Still, it's faster to take him out before he moves.
Once you've killed A, B can be killed with a headshot, but he's in the distance, so aim carefully. Remember to duck back in cover if hit. C will be moving back and forth around the left corner. Wait until he comes across and kill him with a headshot.
After you kill these three, don't leave the cover yet. Move as far right as you can while still hugging the pillar and look left while aiming. You should juuuuust be able to see enemy D up on a walkway. He has a sniper rifle, but he can't get a shot on you. You can get a headshot if you're careful, but he's partially blocked by the wall. Make sure he's dead before you leave so he doesn't snipe you.
Move up to the cover C was behind and get down. Equip your rifle and immediately aim to the left. E will come around for a quick kill. Then get back to cover. F will come from one side or another, usually the left, but check Bourne Vision if you don't see him in a second or so. F can kill you pretty fast if you're out of cover.
Once you kill F, move up the left stairs quickly... G will be coming from the left with a shotgun. Take cover on top of the stairs, or just kill him if you're fast enough. Once he's dead, take cover at the corner, look up, and see sniper H. Kill him.
At this point you should have 2-2.5 minutes left. Don't use your adrenaline yet.
SPRINT down the stairs, around to the left, and back to the right. A flashbang will hit, and you'll be attacked by 3 guys--two CQC and one with a gun. Take the two out as quickly as you can. Try to keep two adrenaline, but if you're having trouble, just kill them. After you're done, run back where you came from, heal quickly, then run back. The guy with the gun will be around the corner. Dispatch him with one of your guns.
You have 5 enemies to go. The first two are snipers; you'll see the laser sights. If you have adrenaline, press up to the wall and use Shooting Takedowns on them to kill them quickly. Once they're dead, move down and into the last area.
Stairs on the right. Two enemies heading down the stairs toward you, and one up on top on the left. The top one will cause the most concern, take him down first. The other two may or may not be a problem. A rifle can cut them down quickly. If you have time, make sure they're dead, because you don't want to die this close to the end.
If you want to get the last passport, it's going to be in the area up the stairs and to the left a bit, on the right edge of that landing, but not up the last long staircase.
Alternatively, if you are running out of time, just ignore the gunmen and sprint straight for the stairs. It doesn't matter if you get the guys or not, once you hit the last set of stairs the final cutscene will play and the achievement will unlock.