The section outlined here is wrong:

https://docs.redhat.com/en/documentation/red_hat_quay/3.15/html/red_hat_quay_release_notes/release-notes-315#skopeo-timeout-configuration-field

SKOPEO_TIMEOUT_INTERVAL as a config parameter doesn't exist. Instead, the interval is part of each mirroring configuration and is configured either through the API or through the UI when mirroring is set up. Additionally,

https://docs.redhat.com/en/documentation/red_hat_quay/3.15/html-single/manage_red_hat_quay/index#mirroring-creating-repo

Under step 5 the indicated field name is Skopeo timeout internal but it should be Skopeo timeout interval.