I brought Season pass with steam but it will not install. Do I have to wait until 2016 for the pass to install? Or is there a way to install the pass?

It's only a placeholder for the DLC as they release. It's not a thing that installs as such.

You'd get no benefit from it installing anyway, there's no new content with the season pass itself. Instead, each DLC as they release will be added and installed automatically for you.

Ah! Thank you for the info.