The company I am helping is 14001 certified. The certification needs to be renewed by September 2018. They have not made changes to meet the new 2015 standards. Are they better off being audited and failing, or letting the certification expire while they make the needed changes?
After September 15th every certification that hasn´t done the transition to the new revision of the standard will not be valid, so you will need to perform that transition before that date if you want to maintain the certificate. If you don´t need the certification for any relevant purpose (such as external provider requirement and so on) you can wait until you properly finish the implementation of the new standard instead of failing the external audit.