look how i calculated mine when i was confused between verna diesel and verna petrol.
petrol price - 70
diesel price - 45
kms to be covered in one year - 10000kms
diesel average - 16
petrol average - 12
petrol's cost - 60000
diesel cost - 30000
difference 30000rs.
i was paying additional 1,50,000 for the diesel.
so my money would have been covered in 5 years, so thats why got the petrol.
i know your case is totally different but still if your daily commute is not more than 60 , you should stick with petrol.
diesel maintenance is high compared to petrol's.
ok i'll recalcuate your's by changing numbers.
petrol price - 70
diesel price - 45
petrol average - 12
diesel average - 16
total kms - 15000
petrol's cost - 87500 , lets say 100000
diesel cost - 42000 , lets say 50000 , considering extra usage and maintenance.
and how much you will pay extra for the diesel ?
for i20 and swift , difference is 1,20,000 and i'm assuming you will take loan , so make it 1,50,000
you will spend 1,50,000 extra on a diesel.
so your money will be covered after 3 years.