War of the Burning Sky (available in pdf at RPGNow, or in print at Lulu) has several adventures at 15th level and above.
At 15th level in particular is O Wintry Song of Agony, wherein the heroes are the point men on a strike mission against a villainous mage's eldritch device. You have to sneak in and take out the key defenders of a valley fortress, and then descend to the torturous prison beneath the fortress, where the suffering of the prisoners provides the power source for the mage's mighty weapon.
It's the 8th adventure out of 12, and we actually designed it so that it could serve as the starting point of a near-epic level (and certainly epic in spirit) mini-campaign. If you were to run it as part of the campaign, there's a whole plotline involving clues to a greater threat and stuff that will matter in later adventures, but if you're running it as a stand-alone, it still works with just slight revision.