My 5E 2024 (5.5E) campaign is reaching its climax. The PCs are currently 15th level, and depending on whether they decide to tie up some loose ends, or decide to rush the BBEG, they will either be 15th or 17th level for the "final battle". A detail that may be important: there is no cleric in the party.
tl;dr: Help me figure out what a 15th level 5.5E encounter chain to stress resources looks like. Thanks!
So without any strong context we can't suggest specific numbers as it comes down to the creature types that make sense.
But look at it from the other side. If a bbeg of some kind wants to ablate attackers, what should they do?
1. A noisy outer perimeter with good perception. Enough of them spread out sufficiently that a single quiet spell can't take them all out. They aren't expected to even be speed bumps but they have horns, gongs, etc to summon reinforcement. Maybe they drop a portcullis, which makes a huge racket. They should have a chance of alerting the defenders prior to invaders of the most likely kind hitting the perimeter. "Of the most likely kind" could be goblins, the group of paladins that keep driving out the bbeg, whatever. Odds are it isnt the PCs. (2% of xp budget)
2. A couple of groups of middle-tier reinforcements that come from different paths. These should have a chance to stop whatever counts as "most likely kind of invaders." Again, that's probably not the PCs. They have the advantage of known terrain and some kind of tactic, which could be as simple as "trolls attack from west, orks attack from east and goblins fire arrows from the rooftops to the north" (8% of xp budget)
3. The reserves. These are a couple of heavy hitters that are expected to finish off whatever the reinforcements are chewing on. Maybe a smaller giant in plate mail, spellcaster, and a sneaky-sniper type. (20% of xp total)
4.the underboss and their personal guard. The person the bbeg will be mad at. (20% of xp total)
5. The bbeg and their guards/minions. (50% of xp total)