Here is what I would do:
The TCO per year for Product "A" is $6.00 ($72/12 years). For Product "B" it is only $4.80 ($72/15 years). So "B" is the better choice.
Note that Product "A" is cheaper until the break even point in year 8, so if you're going to have the product less than 8 years Product "A" is cheaper. However, if this is a long term investment, Product "B" will cost you less overall - have a lover total cost of ownership (TCO).