@irrelevant What's the specification of the hardware of both hosts and also what's the network speed. Especially for the management network interface, as this is the one through which VMs on XCP-ng are imported and also likely exported on VMware vSphere ESXi?
The reason being if the hosts and/or network aren't that quick then the migration of the VMs from VMware to XCP-ng will take longer!
If you can connect the management network to a faster interface then the migration won't take as long to complete.