To get 1.5V you could use a LM317 linear regulator. See schematic, and use a 470Ω for R1 and 100Ω for R2 to get 1.52V. If you want to get the voltage closer to 1.5V, use a potentiometer in place of one of the resistors and adjust it as needed.
Normally the circuit will only draw as much current as it needs if you give it the correct voltage. What are you powering with it? Some devices (e.g. LEDs) need current limiting resistors.
If all you need is 1.5V at 300mA, why use a 12V 6A transformer? A 6V 500mA transformer with the LM317 would be more than sufficient.
**broken link removed**