I was dreading moving sites from v1.5 to v2.5 especially after reading some of the reviews here. However I found it completely painless, thanks to this fantastic software. The migration took with v2.5 - so all my components and plugins worked in the new version - I had some bridges installed as well so was sure they would fail but it all upgraded seamlessly. Can't rate this highly enough.
Also I did not even bother to update to version 1.5.26 I upgraded from 1.5.23 !
Suggest that you are not as cavalier as me though and make sure you back up before running this.