I have a pretty fast internet connection that should allow upload of a 5mb file in just a few seconds. … given various caveats a file this size shouldn’t really take longer than 30 seconds maybe
Typically, transferring a file of this size takes about 4 minutes to iCloud.
Is this due to Apple server congestion? If one has a couple of TB of storage does this still entail a circuitous route, of sorts?
Others may chime-in but in general Apple throttles down iCloud synchronization to what is in essence a background process. Whether it’s to load-balance their servers or to keep your system more responsive or both would require an investigation I’m unwilling to undertake.