CrackBerry Genius of Geniuses
What is this file that's 15mb that you speak of?
I don't know if you're using a MAC or not. But as far as a PC goes here's what I do:
Connect your 8900 to your PC and open up Desktop Manager so that it recognizes your phone is connnected.
-Go to the backup/restore option and click on it
-to the very left of the next screen it gives you there will be the "Backup" option button. Click it, you will be prompted where you would like to save the backup file (by default Windows saves it to "My Documents).
Once that's done, connect the new Bold to Desktop Manager so that it recognizes the phone, hit backup/restore again, but this time choose "Restore" and select the backup file wherever it was saved.
And if for some reason you don't have Desktop Manager installed, I'd download 4.6 from Blackberry's website.