Ensure your composition settings and Render Settings are set to the correct frame rate for your target format/playback device. Typically, a PAL or NTSC framerate would be expected.
Ensure your footage is interpreted correctly at 60 fps. Place the footage in the comp. Apply Time Stretch and set accordingly.
As Andrew alludes, your post is a bit confusing because you don't mention the delivery frame rate. Yes, 15fps is one-fourth of 60 fps, but it doesn't tell us anything about the frame rate you need to DELIVER. Without that bit of information, we're stuck.
Secondly, we're unsure if you want the slowed-down audio to drop in pitch, which it will do when it's slowed down. There are was to fix the pitch (a bit) in audio applications like Adobe's Soundbooth, but you don't want to use AE to do it.
I am content to deliver 15 fps, and I want the sound pitch slowed. Time Stretch seemed to make a mess of my text insertions, but my solution is much more simple. I only needed to interpret my 60 fps source as 15 fps and render at 15 fps. This serves my purposes:
Thanks for your help.
You did the proper thing, then. It works fine. The KISS principle prevails once again.