If any applications are running, the PS4 appears to change the settings for PSN store downloads, artificially restricting their speed. Closing the other applications will remove the limit. There are a few important details:
- Just leaving the other applications running in the background will not help. The exact same limit is applied whether the download progress bar is in the foreground or not.
- Putting the PS4 into rest mode might or might not help, depending on your system settings.
- The artificial limit applies only to the PSN store downloads. It does not affect e.g. the built-in speedtest. This is why the speedtest might report much higher speeds than the actual downloads, even though both are delivered from the same CDN servers.
- Not all applications are equal; most of them will cause the connections to slow down by up to a factor of 5. Some games will cause a difference of about a factor of 100. Some games will start off with the factor of 5, and then migrate to the factor of 100 once you leave the start menu and start playing.
- The above limits are artificial. In addition to that, actively playing a game can cause game downloads to slow down. This appears to be due to a genuine lack of CPU resources (with the game understandably having top priority).
So if you're seeing slow downloads, just closing all the running applications might be worth a shot. (But it's obviously not guaranteed to help. There are other causes for slow downloads as well, this will just remove one potential bottleneck). To close the running applications, you'll need to long-press the PS button on the controller, and then select "Close applications" from the menu.
The PS4 doesn't make it very obvious exactly what programs are running. For games, the interaction model is that opening a new game closes the previously running one. This is not how other apps work; they remain in the background indefinitely until you explicitly close them.
And it's gets worse than that. If your PS4 is configured to suspend any running apps when put to rest mode, you can seemingly power on the machine into a clean state, and still have a hidden background app that's causing the OS to limit your PSN download speeds.
This might explain some of the superstitions about this on the Internet. There are people who swear that putting the machine to rest mode helps with speeds, others who say it does nothing. Or how after every firmware update people will report increased download speeds. Odds are that nothing actually changed in the firmware; it's just that those people had done their first full reboot in a while, and finally had a system without a background app running.
