When you open the project in SSDT 2015, the project will go through a one-way upgrade
. That's about it then, unless you have any custom tools on SSRS/SSIS, where you'll need to source a SSDT 2015 version for your addon.
Just make sure that when you're deploying the project/packages to your server, you have to correct destination server version selected.
Excuse my typos and sometimes awful grammar. My fingers work faster than my brain does :-P
Please always remember to encapsulate your code in IFCode Markup. For example [code=sql] [/code]
to read Jeffs Guide on how to post SQL questions, and get swift and helpful answers from the community