To start the level: There are two starting points that are on the upstairs level.
The one you want to use has crates directly to the left of you, and the soviet is also to the left a bit, straight ahead, barely poking out (you can see it).

The start: Run forward, and grab the soviet. Spin right (towards the railing), and you will see the huge doorway down below.
As soon as you spin right, fire two to four grenades in that direction, and then turn about 145 degrees to the left, so that you are heading away from the nearby stairway (You will be heading towards the whole where the crane thing drops in and out of.)
You should have got a point from killing someone, if not, then restart. (Or if you kill Peabody, your score will show up as if you killed someone, but will say 0).
Turn left, and pick up the soviet ammo by the wall as you head towards the railing over there.
Now is where you will know which strat to use.

First Strategy: Look down below, but don't drop off!
Hopefully you see a couple guys. If so, you will need a lot of luck to pull this off.
Start firing a few grenades as you head to the right and pick up the Rocket Launcher.
opefully you will have killed 2 or 3 people now.
The lucky part is, you have to hope they keep spawning in the room.
Drop down, and kill people with the rocket launcher.
It's not much of a strat, but if you are lucky, you can get a time in the low or mid 40s.
Once you run out of Rocket Launcher ammo, just take out your 2x soviets and shoot grenades at people, then fire a regular bullet or two to stun them for a second, so the grenade blows them up.
Using this complete luck strat, I have managed a run with 16 kills in 41 seconds, which is easily enough to beat the current world record.

Second Strategy: Back to the beginning. You picked up the soviets, fired some grenades at the doorway and killed someone.
You turned corner, picked up soviet ammo. Good.
Now, head forward, and look down again. If you don't see anyone, it's okay. Just grab the rocket launcher, turn around, and head back where you came from.
If you are lucky, someone will be right behind you.
Shoot him with a rocket, and more should start to pop out.
Kill them off as you make your way to the stairs.
Head down them, and kill some more people. Then, head back up the stairs and grab the rocket launcher again. (It respawns at 30 seconds, so if your timer is about 36 seconds or something it will have respawned).
Look down once again, if a few people are down there, drop down and kill them.
Hopefully you will have at least 15 by now, sometime between 50 seconds and a minute.
Since there is no radar, and no set spawns, I can't really help you find them, just use your head... if they aren't in this room and you don't hear nearby firing, head to the big open room with the jet in it.
Chances are, almost everyone in the level will be here, if so, run in firing grenades like a madman and hopefully you complete it. if not, just walk around and find people.
Even if you aren't that lucky, you will still end up with a time of under 1:30...since platinum is 2:00, you will easily get it.

As I said before, this is for PS2, and this is all I can do to help, since there is no consistency in such levels...
However, from my playing experience, these ways can both get decently fast times (or the world record using the first strategy), and are somewhat consistent (compared to most other ways I have tried).

Don't be frustrated if you aren't lucky, you will be someday.