I am using Swift 2.2. But as per requirement of Charts library, I need to upgrade Charts to version 3. Should I migrate to Swift version 3 or I can use this library of version 3 in my Swift 2.2.
Charts v3 is strictly compatible for Swift 3+. (Charts v2 is for Swift 2.3)
And no, you can't mix Swift 2.x and Swift 3.x in the same project. So yes, you should migrate to Swift 3.1 (latest stable).
Note: in the future (Xcode 9), you'll be able to mix Swift 3.2 with Swift 4.0, so it will be easier to transition for this kind of situations.