Our current Reporting and analysis server for TFS 2015 is SQL 2012 Standard. I would like to upgrade to SQL 2016 Enterprise (Join our current 2016 Enterprise environment). What would that process be and will there be any historical data loss?
Is it as simple as remove the configuration for Standard and the point it to the new Enterprise server and then let it rebuild the warehouse and the cube?
outside of the time it takes to rebuild, will I loose anything?
First, check your versions.
TFS 2015 RTM does not support SQL Server 2016.
TFS 2015 Update 3 and beyond does support SQL Server 2016.
Assuming your reporting databases (TFS_Analysis and TFS_Warehouse) are on a totally separate instance of SQL server than your TFS operational databases (TFS_Configuration and TFS_<ProjectCollection>), or are going to be moved to a totally separate database instance, there should be minimal risk. You just update the reporting configuration to point to the new SSRS/SSAS servers and databases and everything will rebuild, no historical data will be lost.
If your intent is to totally migrate your TFS databases to a new SQL server version, it's a more involved process with a higher degree of risk -- downtime will be required and it's wise to do a test migration first.
Regardless, no data will be lost.