Mostly works in iTunes 12.3 (as of Jan 2016)

Currently this app is working for me…. mostly. I’m using iTunes 12.3 and on my mp3 audiobooks it usually works. It’s a little strange or echoey at times, but I get used to that pretty quickly. However, when playing multiple tracks, when one track ends, as it starts the next track there’s often a little weirdness, some repeated and indecipherable words. This Speed-Up app is currently my favorite as it stays playing in iTunes (versus some alternatives that use QuickTime instead — google for itunes script applescript for playback speed to check them out).

brandonjp.com about Speed-Up for iTunes