p1512 is throttle body related
VAUXHALL Throttle Position Adapter Error
VAUXHALL MCP TPS Min Learn fault
VAUXHALL Throttle position signal (TP) - adaptation failure
p1516 is
Throttle actuator control (TAC) system - range/performance problem
clean throttle body and reset ecu by unplugging battery
search on forums on how to clean throttle body
I find it strange that it needs a new ECU when the ECU is showing up some codes and is working how it should do
if the fault comes back then investigate air leaks from around the EGR pipe from the head to front of inlet manifold
also look for the rubber plugs on side of inlet manifold to see they is in place and no air leaks
if your 100% sure no air leaks then move on to Throttle body replacement and lastly switch on accelerator pedal
imo sounds most likely an air leak or faulty throttle body, the faults are basically saying that your pedal position does not correspond to that your of your throttle body
first code says either throttle body , pedal switch or ecu
second code says either throttle body, pedal switch, ecu or immobilizer
if you have a volt meter u can use the TIS checking system but do u know how to gauge ohms, volts etc