Handling a dragon lair’s treasure consistently with treasure parcels

It’s my first time as the DM of a D&D campaign and I’m planning an encounter against a dragon in his lair. Since dragons hoard large amount of treasure, I would like to know how you deal with all this treasure once the PC’s have slain the dragon.

The way I see it, it would make them way too wealthy to let them leave with everything but I can’t think of a logical way to prevent them from taking everything.

I’m considering using a level 15 adult red dragon along with some minions. The party is level 16.