Please find here the latest Drupal 7.15 patch files:

http://drupalmonitor.com/patchfiles/7.0-7.15.patch
http://drupalmonitor.com/patchfiles/7.1-7.15.patch
http://drupalmonitor.com/patchfiles/7.2-7.15.patch
http://drupalmonitor.com/patchfiles/7.3-7.15.patch
http://drupalmonitor.com/patchfiles/7.4-7.15.patch
http://drupalmonitor.com/patchfiles/7.5-7.15.patch
http://drupalmonitor.com/patchfiles/7.6-7.15.patch
http://drupalmonitor.com/patchfiles/7.7-7.15.patch
http://drupalmonitor.com/patchfiles/7.8-7.15.patch
http://drupalmonitor.com/patchfiles/7.9-7.15.patch
http://drupalmonitor.com/patchfiles/7.10-7.15.patch
http://drupalmonitor.com/patchfiles/7.11-7.15.patch
http://drupalmonitor.com/patchfiles/7.12-7.15.patch
http://drupalmonitor.com/patchfiles/7.13-7.15.patch
http://drupalmonitor.com/patchfiles/7.14-7.15.patch

Example: Update Drupal 7.14 to 7.15 using patches

cd /yourdrupalroot
wget http://drupalmonitor.com/patchfiles/7.14-7.15.patch
patch -p1 --dry-run < 7.14-7.15.patch
patch -p1 < 7.14-7.15.patch
drush updb

You may savely remove reject files created during that process:
find . -name "*.rej" | xargs rm

Note
- If you don't know what you do, don't do it!
- Don't do this on production sites!