I was just about to post here, the same thing.
I picked up my new iPhone 6s Plus on Saturday.
Started out fresh, no restore from old phone.
Turned on iTunes Match/iCloud Music.
The Music app shows all my 20K+ songs and playlist.
I go to start a song or a playlist and nothing happens.
This is with full power LTE and WiFi.
It may play about 5 seconds, then hitch for 10-20 seconds and continue.
I am convinced they do zero QC for the music app.
I go to Spotify and Google Play music, everything streams instantly, no delay.
I tried, over WiFi, to download (make playlist offline) and every other song, it gave me an unable to download.
I ended up having to hard boot the phone to get rid of the message.
Clearly something is going on.