Tempo operates on files very slowly. Is there a quicker way?

Example 13 minute vbr mp3 file:

mp3 > mp3 = 18 seconds conversion time
mp3 > mp3 tempo -s 1.5 = 27 seconds conversion time

While I love Sox very much and I appreciate that there's more
processing to do with "tempo", I've got a LOT of files to time-squeeze
and I was wondering if there was a faster way of doing this?
Happy to use another tool for this (Ubuntu). I found "soundstretch"
but that just does wav > wav.
I know I could use something like
https://gist.github.com/NigelThorne/100996 but that's mp3 > wav >
soundstrech > wav > mp3.

Many thanks.