morechildren log notice should notify less often

Now only notifies if user exceeds the "1 request per 2 seconds"
rule in a 30 second period (i.e., 16+ hits in 30 seconds)

r2/r2/controllers/api.py

@@ -1774,7 +1774,9 @@ class ApiController(RedditController):
             g.cache.set(mc_key, 1, time=30)
             count = 1
 
-        if count >= 10:
+        # Anything above 15 hits in 30 seconds violates the
+        # "1 request per 2 seconds" rule of the API
+        if count > 15:
             if user:
                 name = user.name
             else: