Hi @Anonymous
Welcome to Microsoft Q&A! Thanks for posting the question.
I checked and it looks like the "Azure SDK for Visual Studio 2015" is no longer available with Web Platform Installer. You can refer to this link for details on using the Azure SDK for .NET in your application, which is available as Nuget Package.
I would recommend using the newer version of Visual Studio which provides "Azure workloads" through Visual Studio Installer. This should help you get started with the Azure Development faster.
Please let me know if you have any questions.
---
Please 'Accept as answer' and ‘Upvote’ if it helped so that it can help others in the community looking for help on similar topics.