That sounds about right to me. I have about the same amount of nic (to supply two people) and vape the same strength and the calculator told me that it would last over 10 years. I am still contemplating getting another half or whole liter.
Mixing is a first for me after 6 1/2 years of vaping store juice. When my 100mg/ml nic comes in I need to break one liter down to a lower and safer nic level for safety. I guess I could take it to 25mg level and make 4 liters of 25mg and reduce the danger of skin and inhalation exposure. I can keep the other liter at full strength in the freezer and work from the 25mg, cutting it down as needed. Then, I'll have 4 liters of 25mg and one 100mg and the small freezer space gets used up.
I wouldn't have ordered 2 liters if I wasn't concerned about future availability.