I've read several posts on here about the 21-day challenge. Speed is an aspect of my playing that I've never had and would like to improve on.

I'm working on a jazz song - first part of it I can't get is a blazing fast, super clean 15-note run across 5 strings. I decided to make this run my 21-day project to get my speed related technique up to snuff.

RE: the 21-day challenge - how long do you all think is reasonable to practice a 15-note run daily? An hour? As long as I can stand it?

I've seen this method referred to for an entire song (playing slowly but perfectly), but 15 notes over and over would seem to be mind numbing!

Just thought I'd get the boards take before I start day 1 tonight!
I can relate to you on the "mind numbing" the tune I am currently playing over and over now sounds to me like something they would play in a torture chamber... and I'm the one being tortured.

btw in for answer.
I hear ya. It's like repeating a word over in your head, and soon enough it loses meaning and starts to sound weird. Play the same lick over and over and I swear it starts to sound bizarre and you lose the feeling.
I don't think that you really understand where "speed" comes from - you can't just work on "speed" for 21 days. What speed is is hundreds of small, accurate motions, without tension or wasted effort.

You need to examine your playing and work on making every motion neat and precise - there's loads of info in the stickies and such on more specific things.