In the FIFA 16 demo you can lengthen each half by doing the following.
Go to the FIFA 16 Demo folder (most likely located at Program Files(x86)/Origin Games/). Just make sure the file ends up in the folder called FIFA 16 Demo.
Create a .txt file called CL.txt
Inside the file add these lines.
The numer 6 indicates the length of half. You can change this to whatever you like.
Now rename the CL.txt to CL.ini
Now start the demo.
Note that your players’ stamina is set for four minute halves so when you extend the half they will run low on stamina.