The circuit (essentially the wiring and breaker in this case) needs to support the maximum current draw of the Volt. For L2 charging that would be 15 amps for the generation 2 Volt without the increased charging capacity (available only in the 2019 model) or 30 amps with the increased charging capacity.
My recommendation, like others, is to future proof by installing higher amperage capable wiring (at least 40 amps, maybe more) as it is only a small, relatively speaking, incremental cost. For the breaker use a one rated for 30 amps (assuming you won't be using the increased charging capacity of the 2019 Volt). In the future if you need more than 30 amps the breaker can easily be swapped out with one that supports the higher requirements (up to the maximum supported by the rest of the circuit).
