Treyqrch’s David Vonderhaar has confirmed that they will be increasing the XP earned per kill in Black Ops 3’s Search and Destroy mode from 250 to 500.
@ernestandrei It's coming. Going to 500 from 250. XP, not score.
— David Vonderhaar (@DavidVonderhaar) November 10, 2015
It’s not confirmed yet as to when this update will be available.