Here's a catch with low end routers and QoS... When you're gaming... You want it off.
Routers send traffic through multiple protocols and the thing is, heavy traffic needs to get processed by the router to get used. The more services enabled on the router, the more power it'll take. So in the end, your router CPU is going to stall behind when you have multiple services running at max capacity. QoS and Firewalls are typically one of the most CPU intensive processes you have to turn on any router if you want a good service. So effectively you're going to hinder your performance if you turn it on.
However with stronger, faster routers coming out today, it might not be that great of an issue as older days.
If you can set priorities on certain ports, definitely set these higher:
Google this: playstation network port and click on the link that says "Firewall Port Numbers to Play Games Online - Support" (Don't have 30 posts yet, so I can't post links)
If you can't setup port prioritization, UDP might have a better chance with games.
If you do a lot of voice chat, VOIP is a good prioritization.
If you only have Download/Upload (Also known as Downlink/Uplink) prioritization, don't turn it on. Different games will have different amounts of traffic. When your PS4 is off, it's not going to release the bandwidth to other devices either.