Move Dynamics CRM2013 to other domain, move CRM security groups and then upgrade 2013 to 2015

Hi guys.

We have a "complicated plan" to achieve. Here is our current scenario.

We have two domains which are in parent/child relationship: 
domain.local (primary domain)
child.domain.local (child domain)

- Dynamics CRM 2013 on-premises server is a member of child domain so it's FQDN is:CRM2013.child.domain.local.
- CRM2013.child.domain.local has local SQL 2012 version.
- In child.domain.local we have an organizational unit named:CRM2013.
- CRM2013 organizational unit contains four security groups:
PrivReportingGroup {GUID}
PrivUserGroup {GUID}
ReportingGroup {GUID}
SQLAccessGroup {GUID}

Now the idea is:

(1) we need to move CRM from child domain to primary domain. SoCRM2013.child.domain.local will be registered as CRM.domain.local. after we Will join it to primary domain.

(2) we also need to move organizational unit with thoose four security groups from child domain to primary domain.
(3) at the end we wish to upgrade CRM2013 to CRM2015

Any suggestions if we will be able to do that?

Any good tutorials how to achieve all the three steps (1,2,3) without loosing current data and configurations on CRM2013 server?

Thank you.

with best regards

bostjanc