Configuring Transmission for faster download

If you are using a router, make sure that the port used by Transmission for incoming connections is opened in your router (NAT port forwarding). As the other clients are faster, I suspect that they use a port that is already opened in your router.

In Transmission go to Edit > Preferences > Network and set the same port as in the other clients, and disable "Pick a random port every time Transmission is started". You can use the "Test Port" to see whether the chosen port is open.

It's also possible that your router is configured to accept UPnP or NAT-PMP port forwarding requests. If that is the case, you could enable the "Use UPnP or NAT-PMP port forwarding from my router" checkbox (instead of setting the port and opening it in the router manually).

Just a heads up! If you are using Uncomplicated Firewall Wall (or any other firewall) ports 6969,80/udp should be open. Otherwise Transmission cant access some of the trackers. Hence lower download speeds.