Et ceci qui vient de "tomber sur nos téléscripteurs":
Lightroom: CC 2015.2 on MacOS 10.11 crashes[id]=16194849#reply_16194849
Mandhir Bhatia (Official Rep) 13 minutes ago
We are working towards a fix for the issue.

In the meanwhile as told please follow the steps from:

https://helpx.adobe.com/lightroom/kb/...

Thanks
Mandhir