To Reproduce:

1. Attach the script 'DebugLogTest.cs' to any gameobject (uncomment BeginSample/EndSample).
2. Run and connect the profiler.
3. Observe that Debug.Log calls become increasingly more expensive when they are called recursively. Something similar is also noticeable on mono backed, but the increase is much smaller.

Tested on iPad Mini 2 (iOS 8.4) :

IL2CPP:

cpu time/recursion level
8.74ms@100
6.57ms@75
3.51ms@50
1.77ms@25
0.28ms@2

mono:

0.33ms@100
0.27ms@75
0.17ms@50
0.11ms@25
0.08ms@2

Not reproducible in editor - all Debug.Log calls take more or less the same independent from depth