I'm not sure you need it.
You can force your database to run Under any SQL version mode you like until the current one ; it will be using the licence of the 2014 version, but the database itself can run in compatibility mode.
Honestly, I do maintain a fair number of databases on my clients' servers, and this has never been an issue.
Here's a link regarding SQL Server's compatibility modes:
ALTER DATABASE Compatibility Level (Transact-SQL)
Note that you are not obliged to do it with a Transact-SQL script, you can do that with SQL Server Management Studio, if it is installed. You just have to right-click on the database, and select the desired compatibility mode in the property grid (I don't remember if it is on the first or the third tab, though).
Hope this helps. Kindly.