Explanation:

On January 15, 2021, App1 will have only one backup in storage. Yes, this is correct. According to the table, App1 has a backup every 1 day, starting from January 6, 2021, with a retention of 0 days. This means that each backup will be deleted after 0 days, or as soon as the next backup is created. Therefore, on January 15,
2021, App1 will have only one backup in storage, which is the one created on that day1.
On February 6, 2021, you can access the backup of the App2 test slot from January 15, 2021. No, this is not correct. According to the table, App2 has a backup every 1 day, starting from January 6, 2021, with a retention of 30 days. This means that each backup will be deleted after 30 days, or when the storage limit is reached. However, the table also shows that App2 has a setting of "Keep at least one backup" set to Yes. This means that the oldest backup will be retained even if it exceeds the retention period or the storage limit2.
Therefore, on February 6, 2021, you can access the backup of the App2 test slot from January 6, 2021, but not from January 15, 2021.
On January 15, 2021, you can restore the App2 production slot backup from January 6 to the App2 test slot. Yes, this is correct. According to the web search results, you can restore a backup by overwriting an existing app or by restoring to a new app or slot3. You can also restore a backup from a different slot or app as long as they are in the same subscription and region4. Therefore, on January 15, 2021, you can restore the App2 production slot backup from January 6 to the App2 test slot.