Is it possibe to copy all of the python modules from one Windows computer to another computer? They are both running the same version of Python 2.7.12. 
The reason for doing so is that I have internet access on one of them, and manual installing modules on the other requires to much time because of dependencies.
I suppose you mean "copy the python installation from one system to another" (else the answer is: put your modules on a USB key and copy them to the other system).
the best way
The best way of course would be to install Python properly on the other system using setup. But as you said, all dependencies/external libraries that you could easily get using pip for instance would have to be re-done. Nothing impossible with a small batch script, even if you don't have internet, but you would have to get hold of all the .whl files.
the full treatment, portable-style
But if you cannot you can create a "portable" version of python like this:

zip the contents of C:\python27 to an USB key
copy all python DLLS: copy C:\windows\system32\py*DLL K: (if K is your usb drive)
unzip the contents of the archive somewhere on the second machine
add the DLLs directly in the python27 directory.

(those DLLs were installed in the windows system in previous Python versions, now it's even simpler since they are natively installed in the python directory)
The advantage of this method is that it can be automated to be performed on several machines.
There are some disadvantages too:

python is not seen as "installed" in the registry, so no "uninstall" is proposed. It's a portable install
associations with .py and .pyw are not done. But you can do it manually by altering some registry keys.

another method, better
You can have best of both worlds like this:

perform a basic install of python on the second machine
overwrite the install with the zip file

=> you get the registered install + the associations + the PATH... I would recommend that last method.
Last partial method, maybe best matching your question
Try copying the Lib directory only. It's where the libraries are installed. I'm not 100% sure but it worked for me when I wanted to put wx on a python install lacking wx.
Of course you will copy over already existing files, but they are the same so no problem. I let other people comment if this is acceptable or not. I'm not sure of all the installation mechanism, maybe that will fail in some particular case.
Copy python modules from one system to another