Delta Sync Bitmap Sync

We want to preseed volumes for VPGs. Does it go through delta sync or bitmap sync?

We recently did an upgrade a version of Zerto without Vmotion. We have seen that a 2TB machine went into delta sync after VRA upgrade. It took 3 days to complete the delta sync. Was it unusually long. Other VMS which had similar hard disk size also took long time to delta sync.

We have seen that when we create new VPG initial sync time is not that long. It seems that initial sync time is shorter than delta sync. Is it true?

We are having a new data centre. We have two options:

-Presssed the volumes and do delta sync

-Create normal VPG and do initial sync.

After our experience with VRA upgrade we are  not sure if preseed will save us time as we have noticed that delta sync takes really long time.

We have 28 TB of data and 63 VMs. Please advice if preseed will save us time.