Thanks for your feedback @dzenanz We dropped Visual Studio 2013 more than three years ago already: New Build Errors on CDash 1/24/18 - drop support for VS2013 in ITKv5?
So maybe it’s about time to drop VS2015 now. Especially because VS2017 and VS2019 have been around for quite a while now.
However, if it’s really necessary to keep supporting VS2015 for a while, it would still be great if we could already start using the C++14 subset that is implemented by VS2015. The most significant missing C++14 language feature would then be “Extended constexpr”, as I see at the link you added, C++ compiler support - cppreference.com