I gave Mantra a try after using Redshift for over a year.

Running a test with some relatively simple geometry, a couple of displacement maps from Quixel, and 2 light sources my 3000x1500px still image got a whooping 220hrs estimate.

What am I doing wrong? Is it because I need to optimize render settings for displacement etc?

Don't invest time in mantra if you need to it is EOL. Solaris/karma is the way to go and you will get update and speed improvments.

That's a tad harsh. Solaris and Karma aren't fully there, not even close, and are a minefield for a new user.
Mantra is still usable.


Are you using any HDR's in your lights? Convert the texture over to .rat, this is mipmapped Mantra native format.
Easy to open the hdr in mplay and save as .rat, you'd be shocked at how much this impacts render time.

What are you Mantra settings? What render engine mode are you using? Is your displacement bounds, etc set correctly?
Happy to help steer you in the right direction, but I need some more info Duder.


Cheers

L

Yip, defiantly convert your textures to RAT for starters.

One on the big render-time killers is displacement bounds that are to large, if you have verbose level on, Mantra will output a warning in the console how much your geo is displaced. you can adjust according to this. Or another easy way is to make your displacement bounds really low, until you start to see black tearing holes in your render, then increase it a little at a time till the holes disappear.

I also recently found that Noise Level inside the Mantra node, can be increased a lot to cut on the render times. The effects of increasing it was nearly invisible until I hit 0.1 on my scene. You might want to give that a try.