In order to upgrade to the 2015 Outlook client, you must be on Outlook 2010 or higher. As long as Dynamics CRM is not used in offline mode, users having CRM 2013 outlook client will be able to connect to CRM 2015 server. (i.e., no offline capabilities will be supported). However all client machines must have Dynamics CRM 2013 Outlook client at the minimum.
Dynamics CRM 2013 Outlook client can be downloaded from the given link below:
http://www.microsoft.com/en-au/download/details.aspx?id=40344
The recommended process for upgrading your Outlook Client for Dynamics CRM is following. This process will ensure users are able to continue to use Dynamics CRM and their Outlook Clients during your server upgrade to Dynamics 2015.
- Conduct what's new training for all users for Dynamics CRM 2015
- Upgrade your server to 2015
- Conduct a short training for Dynamics CRM 2015 outlook client
- Upgrade all Outlook Clients to 2015
https://technet.microsoft.com/en-us/library/hh699818.aspx
Outlook client for Dynamics CRM 2015 can be downloaded from the following link:
http://www.microsoft.com/en-us/download/details.aspx?id=45015
Hope this helps!!!