I don't use version 15.x myself, so this is more of a guess.
What I think is that the adapterType "pvscsi" may cause the issue. Does "pvscsi" show up as valid adapter type (option -a) when you run
vmware-vdiskmanager -h
What may be worth a try, is to backup w10.vmdk, then change the adapterType to "lsilogic", and run the conversion with the modified header file.
I assume that you have sufficient free disk space to clone (that's what the conversion actually does) the virtual disk.
André
