I wouldn't add the extra confusion of an upgrade into the mix until you get this sorted. If you don't want to start fresh, you can use a compare program to find what files are different from your site vs a clean installation - but you'll need to know what you're looking at, and determine if the differences are from your admin profiles "issue", or from customizations you've made.
If this were me - I would start with a fresh version of 1.5.. i'd do a compare with my site files, and then copy over any edits that you've made FROM your site, TO the fresh install. Most should be done in overrides folders, and will be easily transferred. Any core edits can be identified and transferred over. Then, when you're done, you'll have a complete set of 1.5 files along with your changes.
If you do it the other way around (copying files FROM fresh install TO your site files), it's very easy to miss something, and you could spend months chasing down admin access errors..
As always, all of this work should take place on a local backup of your files, and nothing should be done on live site until everything is tested and working.
Just my 2¢