There is a possible bug in the PS4 firmware that causes slow download speeds related to the round trip time between client and server. Some people have found that setting up a proxy in your house can fix this as it greatly decreases the round trip time.
Of course there are various other factors, and this bug may be fixed by now, although I did hear reports that it was also present on the PS4 Pro at its release.
https://www.snellman.net/blog/archive/2017-08-19-slow-ps4-downloads/
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