PHP CodeSniffer in our Jenkins CI was always one of the slowest tasks as it ran across our whole code base. LB Denker from Etsy wrote a good piece of software called CSRunner which looked to solve this problem by only running phpcs on files that had changed in the last 7 days (or so). It is written as a PHP script that was run from Jenkins.
I took this idea and adapted it to run in Ant. Instead of looking at files changed in x days, it looks at the checkstyle report from the last run and gets a list of files with problems. It merges this with any files that have changed since the last build. In theory it should bring the run time down (assuming you have a low number of files with problems).
I'm open to any ideas on how to improve this as I'm not that experienced with Ant.