What does preparing to copy mean?
Not sure what the 'preparing' stage actually does.  I suspect it could have something to do with verifying that the destination doesn't have files/folders that are present in the source (leading to it having to ask you what to do about the conflict).

In either case, if you are comfortable with terminal, you can use rsync which begins copying immediately and gives you feedback right away.

I would use something like:

rsync --partial --progress -av ~/Desktop/MyFolder /Volumes/MyTimeCapsule/

Good luck!