I know that in Visual Studio 2013 and below there is an option to turn on/off automatic surrounding of generated code with #region at Tools > Options > Text Editor > C# > Advanced> Surround generated code with #region, but that option seems to be removed in Visual Studio 2015...
Is there a way to turn this back on?
You may want to look into CodeMaid at the Visual Studio Gallery. According to the description:
Reorganize the layout of members in a C# file to follow Microsoft’s StyleCop convention, or your own preferences. Automatically generate regions to match. Run on demand or automatically during cleanup.
From what I can tell, this may give you the feature to want.
I'd recommend delving into ReSharper templates. It allows you to specify whatever you would like in your template as well as creating a autocomplete as well.
https://www.jetbrains.com/help/resharper/2016.1/Templates__Index.html