External microphone audio recording on MacBook Pro Mid-2015
I got in touch with RØDE support that replied


  SmartLav+ is not compatible with the newer (2015 - onwards) models of
  the Macbook as it has a different threshold for it's input recognition
  compared to a smartphone or tablet device


Actually compatibility with MacBook Pro (or laptops) is not mentioned in their product's specification sheet, it's designed for smarphones and tablets.

It turns out that the MacBook Pro 2015 audio port is not compatible with many microphones despite the TRRS audio jack.



For anyone that experience this issue I suggest doing the recording with a iPhone (put it in Airplane Mode during the session) then sending the audio file to the mac via iCloud drive.