Unfortunately, I don’t think you can get around the audio delay when you connect the Peloton to the Play:5 using the line-in port.

Not sure how well it will work, but have you considered connecting a Bluetooth receiver to the Play:5 and having the Peloton send audio to the speaker over Bluetooth?

You’d still have the delay on the analog input, since the bluetooth receiver would be connected to the analog line in. 

Make sure you have “Audio Delay” set to “Low”. This limits the audio delay to 75ms, which is the best you’ll be able to achieve.

You’ll find the setting in “Speaker Name” > Line-In > Audio Delay via the Sonos mobile app.