Done a couple of upgrades from SCCM 2012 R2 SP1 to SCCM 1511 and they were straight forward as the prerequisites were in place already.  The notes below were taken doing a new install of SCCM 1511,  albeit into a Active Directory domain that already had the schema extended and appropriate user accounts in place.  In general the preparation required is very similar to doing a SCCM 2012 install.

Environment

• All servers running Windows Server 2012 R2 RTM.
• 1 x Standalone Primary Site Server
• 1 x SQL Server 2014 Database Server (used for SCCM and WSUS databases)
• 1 x Software Update Point Server

Preparation – all servers

As the servers were not to be exposed to the existing SCCM 2012 environment, including the 2012 SUP,  the following updates were applied to the servers in the stated order:

• KB2919442  – this is a prerequisite for Windows Server 2012 R2 Update and should be installed before attempting to install the following updates
• KB2919355
• clearcompressionflag.exe
• KB2919355
• KB2932046
• KB2959977
• KB2937592
• KB2938439
• KB2934018

https://www.microsoft.com/en-gb/download/details.aspx?id=42334

Site Server

• Server Features – .Net 3.5, .Net 4.5, Remote Differential Compression, BITS and WSUS 4.0 Remote Server Admin tool (Software Update Point going on a remote server so need Admin Tools on the Site Server).
• IIS Settings
  • Common HTTP Features – Default Document, Static Content.
    Application Development – ASP.NET 3.5, .NET Extensibility 3.5, ASP.NET 4.5, .NET Extensibility 4.5, ISAPI extensions.
  • Security – Windows Authentication.
    IIS 6 Management Compatibility – IIS Management Console, IIS 6 Metabase Compatibility, IIS 6 WMI Compatibility, IIS
  • Management Scripts and Tools.
• AD Schema already extended – add permissions against the Systems Management container for the new SCCM 1511 Site Server account (remember to allow for descendant objects).
  Obtain the SCCM 1511 source files.
• Download the SCCM 1511 Install prerequisite files (manually by running ..\SMSSETUP\BIN\X64\setupdl.exe SaveLocation from the SCCM 1511 source files)
• Obtain and install WADK 10 (not the 1511 version as there is a widely reporting issue with this version). Features required:
  • Deployment Tools, Windows Preinstallation Environment, Imaging and Configuration Designer and User State Migration Tool.
• Obtain license key.
• Add the Site Server account to the Database Server and SUP Server local admins groups.

SQL Server

• Collation – SQL_Latin1_General_CP1_CI_AS
• SQL Services – run as Local System, not defaults offered.
• SQL Features – Database Engine and Management Tools (Reporting Service will be on remote server at a later time)
• Allow the required SQL Server ports in Windows Firewall (1433 and port 4022)

Software Update Point Server

• Server Role – Windows Server Update Services
  During install point to remote database and not Windows Internal Database.
• After initial install, reboot and run Role Configuration from Server Manager (this bit creates the database etc.)
• Do not configure WSUS itself – just do the automated Role Configuration.
• Reboot and install KB3095113 – https://support.microsoft.com/en-us/kb/3095113.

Install Notes

• Ignore SQL Server-related warnings – only 4GB RAM allocated to my DB server in my lab.
• No to new Service Connect Role (want to do this later)
• Point to existing install prerequisites.
• Don’t use a Site Code that has been used before in the test lab domain!
• Ensure the account used to run the install has the appropriate permissions on the Site Server, DB Server and within SQL Server.

Acknowledgements and thanks for continued contributions to the SCCM community.
http://prajwaldesai.com/sccm-1511-quick-installation-guide/

https://www.windows-noob.com/forums/topic/13368-how-can-i-install-system-center-configuration-manager-current-branch/