Wow, that's a pretty huge jump.
I'd check an imm only command real quick, like goto, and confirm the level using cedit. It's probably still a level 101, I think, command. You'll need to change it to 1501 for it to show up under wizhelp. And do the same for all the other imm only commands as well if you want them showing properly.
If you know you're going to probably go back to a lower level cap I'd suggest making a backup of the commands.dat file in the system dir, then changing level commands. Once you've done all your testing you can put the old copy back and not have too much trouble resetting, if needed, the commands again.
Yeah, I looked at what I originally wrote and went, "Hey, that's not what I meant to say!"