I have a few comments, but you were a bit unlucky there. Why weren't you using the chaotic sabre? If you hadn't identified it yet, anything you get from your patron with the "Thou hast earned a worthy blade!" (or whatever it is) message will be worth using, it's usually a chaotic weapon with a minor hit/dam bonus - certainly FAR better than the broad sword. You also don't seem to have done any quests - the mayor in the outpost (at the top in the middle) gives you a weapon which is better than any starting sword (exept for priests, they get a penalty with edged weapons), and the Bandits quest is doable very early with a melee-type character (bit harder with mages but not too hard for anyone) - Bandits are a lot less annoying when they can only run a few tiles with your money
The wargs quest (actually, you met wargs there - were you doing that one on level 5? unlucky to run into Lagduf at the same time) generates a really scary level message, but one-on-one they're not all that; a couple of magic missiles'll see them off pretty quick, and the reward for that is worth having too - large metal shield +5 if memory serves.
Don't forget to 'R'est between fights, either (unless you're starving or poisoned) - food is hardly any problem at all in the game since you can always buy scrolls of satisfy hunger, find food in the dungeon and visit the inn every time you're in town (it's only a couple of gold to fill you up - bargain), and it's the easiest way to regain HP/mana.
If you get the right conditions, Lagduf can be pretty vulnerable to the explosions of Snaga Sappers - target them with a ball attack (not a missile) when they're in the middle of a big group and you can take out most of his escorts with a couple of well-placed shots. Same applies to Kamikaze Yeeks and the Yeek uniques (more so than the snagas, in fact, since Boldor's so irritating to try and melee with his telporting and summoning abilities).
You probably should've had a bit more DEX than that, too - Chaos Warriors need lots of STR, some CON and DEX, and INT for spellcasting - ignore wisdom altogether and put any spare into CHA, but there's no need to worry about that - you can equip an Amulet of Charisma when dealing with the shops and switch back to another one when you go into the dungeon, and Potions of Charisma are the most common stat-raising ones, appearing after about level 20 (or even in the black market for a few thousand gold - probably not really worthwhile).
Sorry, waffled a bit there. Level 15 should be enough to tackle Lagduf, you might just need to be a bit more cautious.