I'd always assumed that Tor was slower than not using Tor and just put up with it.

Have you tried a new circut or restarting Tor?

I just tested with Youtube and it ran with normal Tor speeds.

If your Debian's process manager is systemd, then

sudo journalctl -f -e -u tor@default  

Also, if I'm not mistaken, your speed can never be faster than the next node that you are connected to. Unless you are running an exit node, that is.

My understanding is, you're routing your traffic through 3 nodes, so the slowest of those 3 will bottleneck the entire process. Unfortunately it's just how Tor works.