The speed of a live usb system is always capped by the transfer speed you have with USB. This is not a 'problem' directly attached to Tails.
This applies to any live OS. USB 3.0 is (kind of) always required to have a smooth (and properly operable) system.
But to say and recommend that OP use Tails to trade clearly shows that those people do not use Tails regularly. Have you tried it? It is frustrating because everything is so slow.
For trading, a bootable USB with a regular light Linux distro would be enough, with or without persistence.
Again, this has nothing to do with tails.
You can install any live OS onto a USB 2.0 device. The speed will be *relatively* equal, less than 40 MB/s.
This is due to the USB port transfer speed, not because 'it is tails'.
Install *any* live os onto a USB 3.0 device (< 300 MB/s) and it will work noticeable faster. Completely independend from tails.
I tried different distros using USB 2.0. Tails was noticeably slower, Lununtu and Xubuntu were ok but lag sometimes. Surprisingly it was the "heavier" Linux Mint Xfce that worked very smoothly.
Plus what made Tails very slow was it had to connect to an Onion circuit and have ALL traffic go through Tor.