A 15 Amp with continuous load should not supply more tha 80% of its 1800 Watt capacity at 120 VAC. A Power Supply should not supply more that 80% of rated load if run continuously.
Also, there are only 6 pcie connectors on most 1200-1300 watt power supplies so it looks like you will need two POWER SUPPLIES. If you run 80% capacity on two power supplies whose wattage total 1800 Watts or less, you will not trip the breaker provided nothing else is on the circuit. If your total power supply wattage is greater than 1800 watts, then the maximum draw from the breaker should not exceed 80% or 1800 watts, or 1440 watts. For a 20 Amp circuit, the values not to exceed are 80% of 2400 watts or 1920 watts. For total power supply wattage less than 1800 watts, the maximum wattage will be 80% of the total wattage of the power supplies with a balanced load and nothing else on the circuit.
Things to consider are that the connections to the receptacles should be tight from the breaker forward thru each receptacle to the load. Extension cords and power strips need to have heavy wiring too, as many cheap ones use 18 gauge wire and will fail resulting in burnt receptacles and plugs. Also, you can’t plug two rigs into the same circuit if you fully load it with either rig.