I realize perhaps that stunning fist may be a balance problem which is perhaps why you put it how you put it. I however disagree.
I believe stunning fist for the monk needs to be adjusted for many reasons. One being that it should not cost 15 Ki to cast, it should be a feat worth taking over Stunning blow, and its essentially unusable as is.
Player to character interaction makes it difficult in combat to use this feat. So I will examine how it does not work in its current form from a gameplay view.
Gameplay
The longer an action takes to activate, the less likely it will be used.
- Cost -
Lower levels: The cost of 15 Ki means the player will never use it in the early levels as the player will never be able to get enough punches in to get enough Ki to land it. This was tested in the game and the results seem to remain the same.
**Test Case
Quest - Butchers Path
Player approaches a batch of 5 - 6 kobolds
Player lands 5 - 8 blows amassing about 20 - 25 Ki.
Problem - By the time they amass enough KI to activate stunning fist, all the kobolds are dead. By the time they encounter another mob of kobolds, the KI is gone.
Note: Stunning blow gives near or close to the same effect and is usable more often than stunning fist. IE there is no advantage to taking stunning Fist over Stunning blow.
Suggested resolution -
Reduce the Ki discharge rate or decrease the cost of the action.
Saves
- A possible save differential arises.
Feats -
Stunning Fist - Taken from the in game description
In game doesn't say it but it is supposed to be
DC 10 + ½ your character level + your Wis modifier
At second level -
10 + 1 + 2 = 13
Stunning Blow - 10 + str modifier.
Starting streangth 18 + 4
10 + 4 = 14
Basically the player is still benefited more at the early levels to take stunning blow and ignore stunning Fist.
At higher levels is the only place I see SF coming into play because the save modifer is much higher at the later levels. I also assume that Ki would be more available at those levels as well.
SB -
10 + 10 = 20
SF -
10 + 8 + 8 = 26
Conclusion-
Unless stunning fist was intended for higher level play only, it would seem the answer would be to decrease the discharge rate or reduce the Ki cost of stunning fist.