The bulk of the work in V2P is the moving of data off the Delphix appliance and onto the ASM storage.
As such, the read IO performance of the Delphix backend storage; the network performance; and read/write performance of the ASM managed storage are all critical.
With so many potential bottlenecks, there is no generic way to respond to this. For the specific context the partner is attempting this in, moving the query to support.delphix.com is recommended.