No, should not need new brake pads and rotors at 5600 miles. On the i3, with regenerative braking/one-pedal driving, should not need a brake job until approaching at least 50 to 60 thousand miles. If some mechanic/dealership is telling you this, go someplace else and have them checked. Shady mechanics will tell owners this, just to make some money, knowing the owner won't know, and will 'trust' the mechanic. Look through the spokes of your wheels and you should be able to see the brake pads and the rotor disks. Brake pads should have at least 1/4 inch of 'meat' on them, and the rotor/disk should have the same. My i3 has 15,000 miles on it and both the brake pads and the rotor are at 1/2 inch or more.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch 427 wheels, EVoInnovate EVSE