If i have a high current (12 amps) passing through my route is it ok to put via on it or to duplicate the route (150 mil on top and 150 mil on bottom)?
Yes, if you have 150mil on top and bottom with both carrying half of the current, then each would get ~6A (or you could consider that both are 300 mil). This would give you a ~10C rise, if that is acceptable then use that. (Remember that it is resistance and temperature rise that determine trace size)
Also Make you do a current/resistance drop on the vias that you use, as they will contribute to loss and heating. (Saturn PCB makes a great calculator for this) Make sure vias are paralleled for the current they carry.
It's better to put 3 or 4 vias for such current and use larger vias or even THT size holes.
It's also better to make the trace as large as possible, if you have spare space, than stick with minimum values given by the calculation. It also depends on copper thickness. Doubling the copper thickness is like doubling the trace width, as high current is concerned.