Will it take longer time to restore VMs from incremental restore points than from full restore points?

The answer is NO.

The virtual full backup technology of Vinchin Backup & Recovery can map the non-full restore points into virtual full restore point. As a result, no matter restoring VMs from which kind of restore points, Vinchin will always directly copy the necessary data blocks from the backup storage to the production storage to restore the VMs, no restore points merging or any other extra work will be done.