Current Calculations in 3-Phase

I'm trying to figure out how to calculate the current through each phase of a 3 phase heater rated at 6kW @ 400VAC. The connections are 3 Live and a ground.
I get P=VI, solving for I I get P/V=I. So 6000/400 = 15. 15A=I. For sizing a 3 phase breaker do I need to divide by 3 to get the current through each leg making it 5A on L1, L2 and L3, or is it just 15 A through each leg?

I also have a single phase heater rated at 2kW at 208VAC. Wire cionnections are L1, L2 and Ground. But this system is being connected in europe (230VAC), so I will have to calculate using Resistance to figure out the power rating at a higher voltage. (208^2)/P=R, then calculate new P and find new current through the wires. R=21.63. Pnew=(Veurope^2)/R=(230^2)/21.63=2.45kW=Pnew. (Pnew/V)=Ieurope=2445/230=10.63 A. Again is 10.63A going through L1 & L2, or divide by 2 and get 5.31 through L1, and 5.31 through L2.

Noone at my work has any input on this. lol. Any clarification is grteatly appreciated