Help with QoS?

So, I'm trying to get my amazon fire sticks to not be slow as a slug buffer wise. I have a tplink router which I'm trying to get to allow first priority to these 2 devices. I played with it a little but last night, but apparently if you don't set a rule for *all* connected devices, it locks out all but the fire sticks or devices with set rules. I want to give these devices priority without having to deprive everything else. I don't want to have to go in and create a new rule if a friend comes over and wants to use their phone on WiFi

How can I give these devices priority *without* locking out others?

My connection allows for up to 15mbps, and my phone and pc gets this speed most times short of network wide issues. It's perfectly fine for 720p even 1080p. But both fire sticks of different models it's not unusual for them to drag right down to 1mbps or less. I suspect this is to some degree Amazon's fault as if I make the point to disconnect everything else it doesn't always get faster being the only awake device connected to WiFi, but I'd still like to remedy this. It's pretty pathetic that with access to 15mbps, I'll try to watch a 3 minute YouTube video which will downgrade to even 240p I think it was before full on stopping. It will eventually resume but interrupted almost without fail

Some things like Netflix I can go in and restrict to 480p, and get better performance... But still I shouldn't need to do this. As well amazon prime nor YouTube allow this on an account basis regardless of device or video, or at all in Amazon's case. I've contacted them, they suggest factory resetting my already new devices.

Also I've done nothing illegal so my ISP have no reason to throttle me. And even at that why throttle only the fire sticks

Any advice would be great !