Substance Painter 2020 layer issues.

I ran into an issue while painting textures within 3 paint layers. It seems that your brush strokes stack up over time causing massive loading times just to click on the layer or load project up. So far I found no ways to force all that data to flatten and default as the image you made so you can keep painting. I could not find any ways to merge layers hoping to do just that. I can't drag layers from photoshop to substance painter.
Fill layers can't be erased or painted on making it only usable for adding a layer ontop to paint with making it hard to fix blends.

Looking for a way to clean that horrible loading time and continue painting.
Currently made a new project with the layers saved out as png to use as fills which isn't ideal.