Transactional Replication Reinitialize
Whether you use a backup or a snapshot, you need to routinely pre-stage the data needed for reinitialization near the subscriber.  The goal is to always  have a backup/snapshot that is within the Distribution Retention Period, and close to the subscriber.

Also whenever you are using a snapshot to initialize a remote subscriber, it's better to copy the snapshot local and use an Alternate Snapshot Location.

Also note that if you have a single subscriber database with multiple subscriptions, you can't initialize from a backup.