You should just be able to take the DTSX's and import them into a new project in VS2012.
The issues you will likely have are more related to the SQL version than the visual studio version.
But you cannot open a Visual Studio 2015 project in Visual Studio 2012. You CAN open the corresponding files (the DTSX or cs for C# projects) in older versions.
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!
I recommend you NEVER run "random code" you found online on any system you care about UNLESS you understand and can verify the code OR you don't care if the code trashes your system.