With 15th level characters, most of the old standbys (crushing room, stone slabs, filling with water, rolling boulders, etc.) are going to be non-events.
"Ooh, another stone slab has fallen! We're trapped! Trapped like ratchets!"
"Put a sock in it, drama queen. One Disintegrate coming up."
The pyramid's creators might have trapped the outer areas with these sorts of traps, which the party will likely blow through, building up a false sense of confidence, as they make it into the inner areas that are trapped with Symbols of whatever and Glyphs of nasty spell X, as well as bound extraplanar creatures or constructs (stone golems in the shape of the guardian of the dead, Anubis, with some sort of cool template to make them a credible threat).
The 'traps' will be more imaginative and potent as they proceed past the 'wimpy' outer traps. Fighting Constructs in a room filled with toxic dust, making the air unbreathable (oh, and poisonous), would be one un-fun example. Why does the toxic dust / 'dead air' not travel? Perhaps the party has to go underwater to get to this room, surfacing into the 'dead air' space from the central pool, creating a natural barrier between the 'good' (dusty, dry, kinda spicey smelling) air in the rest of the pyramid, and this particular room, where the air was purged of oxygen by torch bearing zombies centuries ago. Or maybe there is a spell keeping the air 'bad' in this room. Maybe both. And once the golems are beaten, the keys to the next section can be pried from their head-gear, assembled and used to exit this room and / or get into the sealed inner sanctum, where the stakes only go up.
At some point, swarms of beetles must boil up out of the sand, and fly towards the group in flesh-shredding swarms. Not just beetles, not just flying flesh-stripping beetles, but Fiendish Undead flying flesh-stripping beetles! Yes, this swarm has Spell Resistance, and is pretty resistant to Fire, Cold, etc!
And the big kahuna curse? Anyone who dies in the pyramid rises as a mummy guardian. A half-dozen tomb robber mummies, with varying Rogue levels, wander the pyramid, tasked to make sure that nobody succeeds where they failed!
Finally, the party makes it past the poison and disease, the mummies, the golems, the crushing traps and bewildering passageways, to the great treasures buried with the pharoah, only to discover that he rests lightly. If his treasures are disturbed, he rises to defend them with Outsider-like powers from his 'passed on' status added to his own class abilities, like some sort of Fiendish (or Celestial) Lich.
Random nasty thought. Canopic jars. If one is opened, it attempts to Slay Living / Harm the opener, and if they die from this, their heart is ripped out and occupies the jar. Something extremely big and nasty draws power from this (paragon golem?), and it can be destroyed one of two ways. 1) Beat it to death, while down a party member. 2) Break the jar, which causes it to shut down immediately.
Difficulty? The person killed by the canopic jar can't be raised or resurrected without the jar, and if you break it to kill the Golem, say goodbye to your little friend...
Scrolls of papyrus sealed in ivory tubes that are sealed with molten gold. They have to be pried open, which unseals a guardian curse, genie, poison dust, whatever. Reading the scrolls is not much better, as they are pages from the Book of the Dead, enacting rituals intended to transform the reader into undead guardians of the pyramid!
An admonishment from a Permanant Image to leave this place, or be rewarded with many times your weight in gold! Strange sort of threat... Moving past this image triggers a Polymorph Any Object that turns the triggerer into a statue of gold, but the effect doesn't wear off (and must be removed by Remove Curse from a 19th level caster, or Wish/Miracle type magics). This 'gold' is cursed, and if the statue is carted out by the greedy party, they discover that any part removed from it reverts to it's original form. A sword will become steel again. An arm torn free will become flesh and bone... If enough parts are pulled free that the statue is only half it's original mass, the spell ends and the remainder also becomes flesh and blood (and appears freshly dead from massive trauma and blood loss, since it's had half of it's body ripped away by this point).
