doesnt matter wat size tyres u have on, they will make no different to the ride height as that is totally dependant on the suspension.
so basically your drivers side is about 3cm lower than your passengers side.
and a mechanic has said that there is nothin wrong with the suspension....... basically mate, your drivers side springs are sagging cause they are compressed more than the passengers side due to their bein weight of the driver in there most of the time.
i guess u could swap left springs for right ones, then see if they start to sag to the same level, or buy new ones if it bothers u that much, IMO i dont think there is anythin wrong with them, they just gettin on a bit.