I used decimation master to make a 150k version of my high sub-d model. Then I projected the polypaint from the high sub-d model to the new 150k model. However, there is some texture bleeding. Take a Look, https://skfb.ly/6AQBF. Any way to fix this within Zbrush or should I use substance painter?
The bleeding is caused by your paint not following the new topology, resulting in the new polygon having more than one color applied to it. The only way for that to work is to blend the color across the polygon, between the points. In other words, the points contain the color info; the faces do not. ZBrush then renders color on the faces by blending between the point colors.
The solution is simple. Before projecting, create your UV map and export your base mesh. Then divide the model to have a number of polygons approximately equal to the original model. Now project and create your texture map.