Turned to sawdust, an inch and a half should be more than 3 inches, based on my experience.
In my pigeon aviary I always spray mine with water to decompose them into sawdust right from the get-go. The right amount of water will cause them to break down without making the resulting sawdust feel wet, and with time any water will evaporate and the dry sawdust will dry out the droppings just fine. I find it much more comfortable to walk on the sawdust than on the pellets.
In the cat litter boxes, where the cats themselves provide copious amounts of liquid, I just put in a couple pellets worth of depth (less than inch) and by the time it has all broken down due to the cats’ generous contributions I have 3+ inches in there.
(In my chicken coop I use cardboard shreds because that’s free and also works.)