Priority problem on various ASUS routers

I have a router from my provider, a connect box, basic settings, not accessible directly.

I watch a RTSP stream daily, speed around 10Mb/s, via cable on an Android box.

Same time I'm ussing my laptop via wireless, 4k youtube. The RSTP stream is still smoth.

I've added another router an Asus AC87U.
Same scenario, 4k youtube on laptop, RSTP on tv box. The stream is choppy on box.

Switched the router, AX88U Stream choppy.

Switched on both router to Merlin and/or to QOS, stream still...

Priority problem on various ASUS routers