At those voltages your electrics will go BYE BYE,
The alternator is regulated at 14.5 Volts max - it will stop current flow to the carbon brushes once this voltage is achieved from pole to pole. And it would achieve it whether on idle or running - thats what the voltage regulators job is.
15 Volts will kill a battery in short time - about a month and 16 volts etc will kill it in a matter of hours, not to mention the electrics which will smoke out. I would suggest you check your alternator voltage regulator as soon as possible.
The best grounding solution is to, make a ground cable like this
2 wires to battery clamp (brown if you are a euro nut, black if you are a jap), one about 8 gauge, one about 6 or 4 gauge depending on your choice or requirement - the thicker one should be bolted to the starter ground or near it, and it should branch again to the engine block if required.
the thin wire should be attached to the body of the car. At any suitable place. One ground to the front of the car from engine and one to the bonnet near the hinge to prevent rusting from electrolysis.
The battery clamp aka terminal in Pakistan should be of OEM design - they cost about Rs 450/pair for small ones and Rs 550/pair for large ones. Both made in Pakistan and require a press to attach the wires - They are very very good quality. Look for them at Authorised Hino parts shops (tell them you want original style terminals)
You can also make them with copper pipe - hammer the pipe onto the wires and flatten it then solder the wires to the metal, wrap around a battery terminal for size - and hammer into shape with a rod, drill a hole and install a nut bolt. Looks very nice and clean