Sorry, 50 times not 15. My Haynes manual for the Primera GT (SR20DE engine) says the following:
Faults detected are stored in memory, until the starter motor has been operated 50 times. If the fault is not detected again within this period, it will automatically be erased from the memory. Faults can also be erased from memory by setting the control unit to self-diagnostic mode 2 and then switching it back again.
You can learn how to reset the memory by following this link to the very informative sr20 site
http://www.sr20de.net/engine/ecu_codes.html
I guess your car is too new to be doing this yourself though.