Give some real speed numbers and tell us more about the torrent seeds+peers connected numbers as well as your qBT settings for upload speed max, max connections global and per-torrent, and upload slots.
The torrents may be slow due to bad peers+seeds, or it could be a problem on your end such as ISP throttling of BitTorrent traffic.
For instance, you should be reaching whatever upload speed max limit you set so long as it's <80% of your line's max *IF* you have at least 10 connected peers trying to download from you.
There is a bug in qBT v3.0.10 and earlier that limits total global upload slots to only 8-9, which may be at least partially to blame -- since starting even a single active seeding torrent along with 1 downloading torrent can mean the downloading torrent only gets 4 upload slots.