Thank you Felix. I just would like to have render times similar to the ones achieved by other users.

I just ran a quick profile on what's taking the time when rendering a simple grid, and because there's not much else going on, a bunch of the time is just running the shader, so if you can simplify the shader, that could reduce the time. For example, replacing the default shader with the constant shader cut the time in half. Also, if you don't need the default 9 primary rays sent per pixel, you can reduce the Pixel Samples parameter under Rendering > Sampling on the Mantra ROP. After that, it's a bit too fast for me to easily profile what most of the remaining time is. It may help to increase the Tile Size parameter (under Rendering > Render) to 64. After all of those changes, a 3k*3k render that was originally 20 seconds was down to 2 seconds. It may be that a lot the time left after that is just starting the Mantra process, then preparing and sending rendered tile data from Mantra to Houdini, so it may be faster rendering to disk than rendering in Render View.

As Felix alluded to, many users of Mantra tend to be working in the opposite limit, with lots of geometry and often complicated shaders, so what I described above may sound like cheating, but it may help speed things up for you if you don't need the added complication. The stuff I usually render for my own projects tends to be quite simple, (mostly diagrams), and shadows and speculars can actually be a nuisance, so I've started using a constant shader a lot recently to speed things up and avoid messing around with lights. For still frames, I tend to use more Pixel Samples, and for moving parts, I use fewer, because it's hard to tell that the edges on the diagrams aren't as perfect when the edges are moving.

Thank you ndickson for taking time to help me. I appreciate it.