Q:
Installation from HDD
Not really. The files that came on the GW2 DVD are “old files” since they were finalized before the game was shipped. Since then, there have been several updates that need to be applied before you can actually play the game. So it may be that the game is just installing the patches, and not the entire library.
Check the GW2 folder and look at the file sizes. If there is a GW2.DAT file that’s around 15GB, then you have most of the files and are probably just getting the updates. If the DAT file is less than that, you may indeed be downloading the entire library.
Or just take the CD drive from the other computer and temporarily hook it up to yours.