disk0 - APPLE SSD SM0128G 121.33 GB (Solid State - TRIM: Yes)
Internal PCI 5.0 GT/s x4 Serial ATA
disk0s1 - EFI (MS-DOS FAT32) [EFI] 210 MB
disk0s2 [APFS Container] 121.12 GB
disk1 [APFS Virtual drive] 121.12 GB (Shared by 7 volumes)
disk1s1 - M************************* - Data (APFS) [APFS Virtual drive] (17.96 GB used)
disk1s2 - M**************** (APFS) (15.41 GB used)
disk1s3 - Preboot (APFS) [APFS Preboot] (271 MB used)
disk1s4 - Recovery (APFS) [Recovery] (1.12 GB used)
disk1s5 - VM (APFS) [APFS VM] (2.15 GB used)
disk1s6 - Update (APFS) (4 MB used)
disk1s7 (APFS) [APFS Container] (15.41 GB used)
disk1s7s1 - M****************** - Data (APFS) [APFS Snapshot] (15.41 GB used)
The computer has a 128 GB SSD Drive which, sadly is the smallest of small SSD Drive that Apple should have never put on the market
Then, from you report, the disk1 [APFS Virtual drive] 121.12 GB (Shared by 7 volumes)
Normally, it should be showing Shared by 6 volumes
You may what to refer to link below regarding Extra Snapshots which under septic situations can be removed
If so, at least 15.41 GB will be returned as usage space
View APFS snapshots in Disk Utility on Mac