Mac-to-Mac VPN Xcode speed: AFP vs VNC
You are basically being punished by having put your project on a slow, slow harddisk.  There is much more network traffic than you think when working with files remotely and on such a slow connection you will really feel it.  Most modern IDE's expect files to be locally available, not on a slow, remote drive.

I would suggest looking into mirroring your work files between your work and home machine as needed.   To my knowledge there are two basic approaches:


File synchronization:  Use "rsync" to move changed files back and forth as needed.  This is good if you need to edit locally, but compile remotely.
Source repository:  Work locally until you have a satisfying result, commit the revised sources locally to the repository, and then update the remote sources from the repository.  This works well if you can work fully locally.


Please report back what worked well for you.

(Incidentially this is why Remote Desktop for Windows is such a good thing.  It uses the bandwidth very, very well making Windows usable even over a very slow connection, and allows for a much larger display than on the remote host)