Bryan, from what I’ve read, 12-15 feet is an awfully long distance to cool, especially if it is 12-15 feet each way, making the total circuit (using the diagram below) a minimum of 24-30 feet. Additionally, I am not certain that the circuit will be the best method, as it will allow air to circulate around the beer lines all the way to the tower (good, if it works), but probably not up the tower to the tap, at least not with the same efficiency (bad, as this will cause a warm spot in the line).
This is the same advice as in the post in the General Questions area: Where to put Chest Freezer? topic. In that post, I put a number of links that state that short of using a glycol system, a consumer blower is not going to have the power to move that much volume, and a commercial pump is going to run too warm for the refrigeration to compensate. I am not sure if the fact that you intend to use a chest freezer (converted I assume, as freezing the beer will not help either) has any bearing on this, but I think that it is still going to be too long. Is there any way to get the chest freezer closer to the bar.
According to the article, it looks like 5 feet is really the maximum of what you want to go for, and though I assume that there is some play in that figure, I don’t think that going 3 times that is going to work out so well.
EDIT- I just realized that your post came prior to my initial reply, but will leave this here in case anyone else needs to reference it.