I recently upgrade parrot on usb persistance and it full over 10 gb of disk space, same after apt autoremove. This is not normal to take as big for and upgrade. I look for a solution for recuperate at least 5 gb. I don't really use the parrot tools aswell.
A Linux live USB drive is normally a blank slate each time you boot it. You can boot it up, install programs, save files, and change settings. But, as soon as you reboot, all your changes are wiped away and you’re back to a fresh system. This can be useful, but if you want a system that picks up...
Since you're not using all of the tools:-
You could just install Parrot or better yet install Debian 10 Buster.
Debian is pretty rock solid and it has ran great on all of my Linux boxes for years.