When will voyager 2 leave the solar system?

That kind of depends on where you consider the boundary of "the solar system" to be.

It's currently in the "heliOSheath" and will probably reach the heliopause... which is one reasonable definition of "outside the solar system"... within the next ten years or so. Voyager 1, which is further away and moving faster, is expected to reach this boundary in about 2015, but Voyager 2 reached the heliOSheath significantly closer to the Sun than Voyager 1 did... this boundary appears to be "dented" in the direction that Voyager 2 is heading.

Voyager 2 is well outside what most non-scientists think of as "the solar system" already... it's over twice as far from the Sun as Pluto is, for example.