if you add up your lease payments x 48 months then add residual value + tax you will notice it comes pretty darn close to what you'd pay if you bought instead of leased.

and since you put on low mileage your car will likely be worth a few thousand more than what the residual + tax is .

once lease is up , buy it out(dealers will refinance for you) and you have a bargaining chip for trade .
or just buy it out and keep it if you are happy with how its running.