An observation* - Pregen characters are never as well equipped as characters who have fought their way through.
The best items are a little weaker (15 th level would normally have a +3 (Maybe 2 or 4) main weapon, a couple of +2 backup weapons (eg, bow for a fighter with a +3 sword).

And they lack the depth. Everyone should have magic armour and shield (or bracers etc), everyone will probably have some sort of ring (or 2)

+ a few other bits and pieces of permanent magic - girdles, boots, amulets etc
+ my experiance would suggest about 1/2 doz potions
+ scrolls for those who can (wizards and clerics probably have 2-3. I'm pretty sure most rogues would have about the same, but I'm less sure that's right for this edition)
+ a wand/staff or 3 for each person who can use them.

* I played more modules of 2nd ed than AD&D. My AD&D was more D&M created. But the observation seems to work well across editions