Have them check the memory and CPU allocation of the hypervisor, make sure its not overallocated. Make sure the partitions for stroage are aligned (see here: https://blogs.vmware.com/vsphere/2011/08/guest-os-partition-alignment.html) . Install tuned, and enable the throughput performance profile. Oracle has a problem with transparent hugepages, postgres may well have the same problem, so consider disabling transparent hugepages. There is no reason why performance on a VM would be worse than performance on a physical server.
