Before buying the new brake pads, first you have to make sure that its existing brake are really done or bad.
as you said you drove Santro and Vitz before...., then driving mehran would not be so easy for the first few days specially.
once i came home on my crown and a mehran was wrongly parked outside by some of our guest and he requested me to park it aside by myself. He gave me key and i start the mehran. I was pushing/pressing its brake padel like hell but it was not working good. i told that guy that you should check its brakes because these are not working well, but he said these are perfect. After some time we went in his mehran in the market and he said the brakes are working perfect.
(hope you can extract the message from this short story)