Looking at migration to BizTalk 2016 from our existing 2010
The big question ... what is the upgrade process for existing BTS 2010 solutions?
Is it as easy as opening in VS2015? similar to ... Migrating BizTalk 2010 source to 2013
From 2010, yes, it's pretty much open and migrate.
The most notable change is to compiled xslt which changes some specific behaviors. So, you will have to test all your maps specifically. If there is a problem, you can either refactor it or set a flag to use the old interpreted transform.