Move the minimum iOS version from 13.0 to 15.0 (#86)

Author: jkingok

cookiecutter.json

@@ -12,7 +12,7 @@
     "version": "1.0",
     "build": "1",
     "python_version": "3.X.0",
-    "min_os_version": "13.0",
+    "min_os_version": "15.0",
     "uses_non_exempt_encryption": false,
     "_copy_without_render": [
         ".gitignore",