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It depends entirely on how much IPv6 traffic you're processing, but you can expect both to increase (memory more so than CPU)

Due to the size of IPv6 headers (40 bytes) compared to IPv4 (20 bytes), IPv6 connections will take more memory to track.
This will mean less IPv6 connections can be tracked compared to IPv4 (again, exact number depends on configuration).
Routing table entries will also take more memory as a result (be it dynamic or static).

Because there is less room in a 1500 byte packet for data, you may receive more IPv6 packets for the same amount of data sent via IPv4.
That will ultimately have an impact on CPU, but far less than the impact on memory.