I noticed that when I download a large file over Wi-Fi my Airplay stream stutters and then dies out.
I am just streaming audio from MacBook Pro 5,3 (e.g. Spotify) to my Airport Express.
At the same time a Xiaomi Redmi 2 and a Huawei P9 are often connected to the Airport Express. No heavy traffic is going to them (only some WhatsApp and browsing) 

During the download, data is coming in at around 6 MB/s, and I see that 200 KB/s is going up.

When I check my Wi-Fi statistics I see I have a transmission rate of 145 (Mb/s I assume), which converts to 18 MB/s so I should have plenty of headroom.

How can I give Airplay priority on my network, such that there's always plenty of bandwidth available to stream?