CRM Up-gradation From 2013 to 2015

Hello,

I have upgraded CRM  4.0 to CRM 2011 to CRM 2013. We are using below Organization Services for O-Data and Custom Code for creating and updating data into CRM from Custom Applications.

For  O-Data  -- https://XXX.XXX.XXX/XRMServices/2011/OrganizationData.svc

For Custom Code -- https://XXX.XXX.XXX/XRMServices/2011/Organization.svc

Now I am planning to upgrade CRM 2013 to CRM 2015. So  do I need to change my Organization Service in current customization or will the above work for CRM 2015?

What changes are required to upgrade CRM 2013 to CRM 2015?

Also, the CRM 2011 Organization service is going to be deprecated. So what is the replacement for it or do we need to use the API provided in CRM 2015?

Thanks In Advance.