FYI FWIW...
I set the ILR to ON ("1") and with v1.69 installed, a level 10 fighter was able to get Barun to make the +4 version. It is unequippable (red), though, as expected. The engine diagnostic only reports that the level is insufficient to use it, not specifying the qualifying level. I am assuming that the qualified level has been determined by the OP in a previous game.
So, since it's the current save using the ILR setting, my suggestion is to make the flail anyway and ID it, then stash in inventory until reaching the level requirement (or any of the other high-level weapons/armor you can forge). Surely, if Level 15 is what is required, that is easy enough to reach unless many of the XP opportunities have been skipped. End of game level should be no lower than 16 even with a henchman, summon and familiar/anml companion partaking in the majority of the combat episodes.
edit: Oh, btw... you could save your character at the end of Ch 3, change the ini to turn off ILR (if you haven't already), then start a new OC game at Ch 4 using your pregenerated saved toon. Any of the high-level weapons should now be usable at any level (assuming you have the proficiency, naturally). The only caveat is that there probably won't be a henchman appearing since the module carries forth the one you had in Ch 3 which won't be loading the new chapter (4). Up to you. Seems like a lot of finagling to me just to use a +4 flail. <-----totally unnecessary. See Shadooow's comment about ILR and saved games. It's EZ PZ.
