Level 16

Total Experience Required 31,436 [confirmed]

Level 100 progress: 0.46%

This is roughly:
Killing 105 people in Warzone, or...
Killing 107 people in Execution, or...
Killing 89 people in Wingman, or...
Scoring 22,455 points in Guardian, or...
Scoring 68,340 points in Annex, or...
Scoring 41,364 points in Submission.

Horde (TU4)

Completing 158 waves on Casual, or...
Completing 105 waves on Normal, or...
Completing 79 waves on Hardcore, or...
Completing 63 waves on Insane.

Or a combination of the above. Have fun!