Even if the path structure doesn't match, you can make a symlink. It can be done on Windoze, I'm sure other OSes also have that.
About taking that long - it gets data from various nodes so the download is not continuous, also it has to "crunch" that data (check validity and probably other operations too). And I think that's over 150GB of data.
symlink in *nix is called a softlink..
ln -s
as for the sync speed: OP is talking about btcd. In my experience, btcd is a lot slower than bitcoin core when it comes to syncing (i'm currently close to giving up syncing my own btcd node and switching back to bitcoind, since my node has been syncing for 2+ weeks now).
IIRC correctly, it has something to do with the fact that btcd doesn't multithread it's sync process... When i noticed the slow sync speed, i remember i found the rationale behind the slow sync speed somewhere on a github ticket, i'm just to lazy to try to search the ticket again