Updated min clang version support to 15

Version 14 may still work, but we'll only be actively supporting 15+

README.md

@@ -160,7 +160,7 @@ auto ec = glz::write_file_json(obj, "./obj.json", std::string{});
 - Requires C++20
 - Only designed and tested for 64bit little-endian systems
 
-[Actions](https://github.com/stephenberry/glaze/actions) build and test with [Clang](https://clang.llvm.org) (14+), [MSVC](https://visualstudio.microsoft.com/vs/features/cplusplus/) (2022), and [GCC](https://gcc.gnu.org) (11+) on apple, windows, and linux.
+[Actions](https://github.com/stephenberry/glaze/actions) build and test with [Clang](https://clang.llvm.org) (15+), [MSVC](https://visualstudio.microsoft.com/vs/features/cplusplus/) (2022), and [GCC](https://gcc.gnu.org) (11+) on apple, windows, and linux.
 
 ![clang build](https://github.com/stephenberry/glaze/actions/workflows/clang.yml/badge.svg) ![gcc build](https://github.com/stephenberry/glaze/actions/workflows/gcc.yml/badge.svg) ![msvc build](https://github.com/stephenberry/glaze/actions/workflows/msvc.yml/badge.svg)