The maximum lifespan for a mini schnauzer is 15 years so if you keep the mini schnauzer healthy and get regular vet checkups for the dog then the mini schnauzer should live up to 15 years but sometimes can live for 16 or 17 years but that is rare.
Some mini schnauzers may only live as long as 12 years if they have some health problems or are not exercised regularly.
Make sure to get the mini schnauzer enough exercise, feed it healthy dog food and get it regular vet checkups and the dog should live at least 15 years.