"If a company is following the 2008 version of ISO, an audit is supposed to be in March, It must be done according to the new version (2015). What is the standard procedure? is it possible that the old version keeps running till the end of the year & new version to take over from the beginning of the new year? In this case, the audit is to be performed in accordance to both standard!! If not, what is the practical solution?”
You should contact your certification body because they are the ones that can help you more with that question. Some certification bodies stop issuing ISO 9001:2008 certificates after September 2016, and most importantly ,last October the International Accreditation Forum decided that certification bodies will no longer certify QMS according to ISO 9001:2008 after 15 March 2018. After that date, even if your QMS is according to ISO 9001:2008, certification bodies will conduct all ISO 9001 initial, surveillance, and recertification audits to the new version (ISO 9001:2015).
The following material will provide you information about transition: