SQL Fast database restore with Azure Virtual Machine instant recovery snapshot and SQL in Azure VM? I have a large database. If I want to restore to a point in time using a full back up, it takes around 4 hours + time taken for transaction log restores.

I also have VM image instant restore snapshots taken on Azure daily. The restore of a VM image by replacing existing disks takes only 20 minutes.

It is known that transaction logs cannot be restored unless the most recent full back up is restored.

Lets say I sequence my backup jobs in this order:
1. Full SQL Backup of the database taken and stored on Azure using "SQL in Azure VM" feature of the Recovery vault
2. Azure VM image instant restore back up following it (there may be one hour in between with transactions occurring)
3. Transaction log backups using the same feature on Azure as #1, every 15 minutes

Then if we have an outage, can I do a faster restore by restoring the VM image? Would I be able to skip the full backup restore and directly restore only the transaction logs in this state of the VM? Is this a sound theory?

The LSN of the database should be at the state when the VM snapshot was taken. Would it be a problem since the database would come online immediately and the LSN would change before I can take it offline and do a restore?
Then if we have an outage, can I do a faster restore by restoring the VM image? 


No.  See my answer here. Is it possible to restore a database with database backups starting on top of a restored server point in time snapshot that is out of date?

You can't attach a database without crash recovery, and you can't perform a crash recovery without the transaction log file.  Log backups cannot be substituted.  

If you put your database files on Azure Page blobs, instead of on an attached disk you can use File-Snapshot Backups for Database Files in Azure.