I am in Australia and using a Mac Pro 5,1 (and prior to that a 3,1).
Short answer is - no - 15A is not required. 10A only - otherwise the Mac Pro would have come with a 15A socket/plug (which in Australia looks identical to a 10A plug but the vertical (neutral) blade is wider and won't physically fit into a normal 10A socket).
As the PS is 980W, 15A not required as the max current draw at 240V cannot exceed 10A. (980VA(W) / 240V = 4.08A.
A 3000W power supply will exceed 10A - therefore a 15A cord/plug/supply is required - (3000VA(W) / 240V = 12.5A.
If you manage to populate your MP with devices that draw the full 980 W of the power supply (not sure that is even possible and the failsafes in the MP would likely shut it down anyway), your standard 10A power socket/cord will cope fine. (Plug in another 1 or 2 heaters on the same circuit, however, and likely the circuit load will exceed 10A pretty quick and trip the circuit breaker in your electrical board),
Edit - and just to be clear - the power cables in your house are usually specced at a significantly higher Amp Rating than the actual Amp that they are rated for. For example - you standard power circuits cable is probably something like 20A rated cable (i.e. wire thickness and insulation can cope with up to 20A current flow before it overheats, starts smoking etc.). The 10A "limit" is regulated by the (old days - fuse wire) circuit breaker in your power board and this will trip and cut any power flow down that circuit should the load exceed 10A (and well before the 20A that the actual cable can sustain).
This is of particular notice for your standard Oven installation - Ovens required a beefier circuit and are commonly on dedicate circuit/wiring to your power board that has (I think - could be wrong) a 38A fuse/circuit breaker. And the cables for that circuit are rated for this (thicker etc.).