I'm not good in the terms use to express it, but just trust my own ears. The first hours out from box after I got the right fitting, I felt the bass is very heavy like my Monster Turbine and the high is a bit too sharp for my liking, not very bad sounding but not impress either comparing with the Turbine.
After over night burn-in, the next day with the same music tracks, I felt the sound open up more and the bass much better not over powering, and high is smoother then the day before. I liking it more and more now.
If you like to read more impressions, you can go to the link below, may be a interesting read for you.
http://www.head-fi.org/forum/thread/542003/new-shure-se215-first-impressions
As for burn-in files, you can read and download from below link:
http://www.burninwave.com/
Hope this help.