How often Outback model refreshed?

Sorry I can't answer your question, but yes there is a Wikipedia entry for the Outback.
Subaru Outback - Wikipedia, the free encyclopedia

Since they just made an engine change to the 2013, your guess of 2015 for a totally new model seems likely.

It all depends on the market. Subaru has always had its own niche so it can pick and choose when it wants to make a change. Nowadays manufacturers are designing vehicles with more future proofing in mind. You'll see mid cycle refreshes featuring things like you get with the '13 update. Don't always count on them though. If a vehicle is selling well in a weak market it can soldier on for awhile. Take the WRX for example. The Impreza got a redesign but the WRX is still running on previous platform.

In other words, we can't predict when a vehicle will get a redesign but you can keep an eye out on the internet and in periodicals for news and rumors.

The current Outback is selling well enough to where it could remain in its current form until 2016.

It'll likely be for the 2015 model if they keep true to form.