5x3w led lamps power supply
12V marking on your lamps imply they require regulated voltage, so you need 12V supply. You have 5x3W laps, that in total is 15W, hence you need power supply that can handle more than 15W, say 20W, so that there is some safety margin, which expressed in amps would be 20W/12V = 1.6(6)A, or in nice round numbers - 2A or more.
So answer is 12V 2A power supply is what you need. And yes, you have to connect them in parallel.