The P1A15 code is thrown when it takes too long to charge up the voltage (to 220V or more) of the big capacitor located above the FETs in the bottom of the EMCU (electric motor control unit, aka drive inverter). The capacitor could be leaky or the precharge resistor could be open circuit or too high resistance, or there could be some extra load on the pack (like the heater is shorted or commanded ON), which prevents the precharge from reaching either the voltage or time requirement. Step 7 checks to measure this voltage.
Of course before getting to step 7, did the mechanic run step 3, check main fuse? Removal of several cover panels is required to get access to the main fuse plate on the bottom of the pack, but once there, a check of the heater and the A/C fuses could be done also.
But a quick way to check both the fuse and the voltage is to pull the top cover plate off the motor controller and measure the voltage directly at the input terminals with a voltmeter.
If there is no voltage, then the main fuse is suspect. If the voltage rise is slow or below the expected 220V, then the EMCU is suspect.
On a more basic level, do you know that the pack is good--what does the 'fuel' gauge and range-remaining read when key is switched to 'ON' ? Does the car take a charge when you plug in the charging cable?