well i'd say its a legitimate draw, if he can continue to check you without you stopping the checks, its endless and would amount to a draw.
What happens if...

if however you were able to get out of check say by moving your king over and on the 16th move you would be out of check, then I don't think you should be thrown into a draw without agreeing, only if you cannot stop the checks
Alright so I was playing on Yahoo Chess (wanted to see how much better I had gotten after playing here) and I was playing someone. Now I had a pretty much winning position already so the other guy just began to pointlessly checking me. Just back and forth with his queen with no other motive. After about 15 checks yahoo said the game was a draw. I've read about the threefold repetition but isn't that only if I agree to call it a draw? So am I missing something? Was that a cowardly way to draw or does yahoo just suck with rules?