What BT client are you using?
Do you have a static IP address?
Are your listening ports open, Both UDP and TCP?
The files that you are trying to download:
How many seeds are there?
How many Peers?
Whats the availability of the file?
If you use a VPN then it is normally slower because of routing issues,
Well, I am not going to insult your intelligence by asking for you to check the number of seeders and leechers on the torrent you're trying to download, because I'm pretty sure you already know that. I don't know Ian asks what torrent client you're using, because for all practical purposes, it doesn't make a bit of difference which you are using. I don't know exactly what your problem might be, but I can tell you a few things that might be helpful.
I don't know what VPN you are using, but some VPNs have an option where you can either route just your web browsing through it, or route everything through it, which includes applications and bittorrent. When I route my torrents through VPN, my download speed has never been limited, I've gotten the entire bandwidth that I've paid for. In fact, for years in China UDP trackers for torrents have not worked for me, only HTTP ones. When routing bittorrent through VPN, UDP works, which means more connectable peers, so you might want to check if you are indeed routing your torrents through the VPN and not just for your web browsing.
Secondly, I recommend the website www.torrentz.eu for torrents. I personally think that piratebay is pretty crap, but torrentz.eu is a torrent search engine. It searches for torrents from many torrent sites (including piratebay) so you get many more options. It also gives a list of trackers with seeder and leecher info for each tracker on every torrent, so you can add extra trackers to the torrent you want to download, if necessary.
Maybe your torrent client is just not properly configured, but all I know is that I'm in GZ too and torrents are downloading full speed for me.
+1 for KAT
+2 for kat.ph. My go-to public site.
I recommend using private trackers, such as hdchina, ccfbits or torrentday. More seeders, less leachers.
I regularly get speeds in excess of 1-4mbps.
mine works fine, on three computers. i dont use a vpn, and normal, cheap cable internet to my apt. i just set "bandwith allocation" to High,and i'm happy.