Hello ,
If VM is running on snapshots then the performance will be affected. this is by design. Please follow the best practices for Snapshots from Vmware.
1. Do not run the VM on Snapshots for more than 72 hours.
2. Do not keep more than 1 snapshot for performance.
3. Schedule the backup at night in off production hours.
Please follow the above best practices for Snapshot based Backups.