I was able to upgrade from MSVC++ 2012 to MSVC++ 2015 despite our continued non-usage of Unicode in MFC. I was sent this note after
I posted the question in the Microsoft store:
"Lynn, I use VS 2015 to develop non-Unicode apps. In the project settings on the General page, there is a setting called "Character
Set". You can select "Not set" for this value and non-Unicode versions of the library calls will be made. I use this for C++ native
applications, I don't know if this will solve your problem but I thought I should mention it."