Q: Why is booting from USB so slow and can it be made faster?
A: It depends on your Mother Board. If it only supports USB 1.0 then it will be slow and there's not much you can do except switch to the Full platform and install it on a harddrive.
Some Mother Boards that support USB 2.0 will only boot a 1.0 speeds. Sometimes there are BIOS settings that can be used to change this behavior, sometimes not. The same counts with USB 3.0.