Using this script https://greasyfork.org/en/scripts/427686-itch-io-bundle-to-library with tampermonkey should help speed it up.
Tampermonkey:
Chrome: https://chrome.google.com/webstore/detail/tampermonkey/dhdgffkkebhmkfjojejmpbldm...
Firefox: https://addons.mozilla.org/en-US/firefox/addon/tampermonkey/