An RPO of 24 hours means a nightly backup is enough; at worst a day's work is lost. An RPO of 15 minutes requires frequent snapshots, log shipping or replication. The RTO determines how fast hardware, restore and verification have to happen.
Both values are business decisions, not technical ones. The smaller they are, the more expensive the solution. Set them per system: mail and file storage usually need tighter values than an archive.
An RTO is only worth as much as the last restore test. Only a test reveals that restoring 2 TB from cloud storage takes two days, or that the key for the encrypted backup is missing.