Portal/Chamber 15

First room
The first room introduces you to the double fling.

Place an orange portal on the push board above the entrance, create a blue portal on the wall, and enter. As you fall through, create a blue portal on the floor below on the checkerboard, and the next jump will give enough momentum to pass through the force field.

Second room


The second room has a pellet that needs to cross two forcefields Get a portal on the burn mark, along with a corresponding portal that leads the pellet to the other side of the room. Then, run to the receiver, and shoot a portal in front of both the pellet and the red light above the receiver.

Make sure you took out all cameras, since you can't return once you go up the lift.

Third room


As with the first room, you have to perform a double fling; however, you can't start the fling within the same room because of the flooring. Instead, you need to head to a side room to the left which has a staircase where you can create a portal and jump. When you go through, quickly fire the second portal on the checkerboard and you will be thrown through the force field.

Next, you have to perform a double fling to cross the second forcefield.

You are now in a room where a pellet is bouncing against an angled wall, and scorching the side wall. Shoot a portal at the scorch mark, as well as the wall opposite of the scorch to bring the pellet to the receiver, and double-fling yourself back by one sub-room.

You now need to cross a conveyor belt that's moving backwards, and a misstep will drop you into the water. The easiest way is to shoot portals on the wall within the corridor, and go through the portal you placed at or near the entrance when you can advance.

Fourth room
A pellet launcher is firing a pellet downward, and the receiver is blocked by a double door.

The doors are opened by the buttons in the side rooms. To open both at once, you need to get a portal in both rooms to quickly press the two buttons. Then, shoot the wall opposite of the receiver followed by the scorch mark on the ground to get the pellet into the receiver.

The lift for the chamberlock will lower, and you can proceed to Chamber 16.