Compare NX lenses and tips

A question about the NX lens. I have Samsung NX300 E NX3000. The lenses I have are 16-50mm 1: 3.5-5.6 - 30mm f2 - 16mm f2.4 - 50-200mm - 18-55mm. I am very pleased with the quality of my photographs but if I can try to improve. My questions are 2. 1) Do the same environmental and light conditions (daylight) make a photo with any lens at the same focal length and with the same settings the image quality changes a lot? 2) I've read from several parts making photos (especially in the evening with artificial light without flash) with a lower resolution (eg 6 mpx instead of 20mpx) can greatly reduce noise and thus improve image quality.
Do you have answers based on your experiences? I ask this because I'm waiting to buy a new lens and then I wanted to evaluate the convenience for the purchase. Thank you all.

Changing your camera setting from 20mp to a lower resolution like 6mp won't help with low light. It won't do anything except make a smaller image. You need brighter lens. Lower f-stop lens needed to make photos in low light with less noise.

You can do something, to reduce the noise by "resample".

Let say you have an 24Mpix photo, which looks more or less OK but it is too dark.
If you enhace exposure even only by x2-x3, it will become very noisy.

What I do in such cases, I increase exposure with 1.5-2 so the noise is still low, then reduce resolution with resample, let say two times (from 6000x4000 going to 3000x2000) and with the new image you can increase exposure once again with 1.5-2 and the noise will be still low (it was reduced by resample when an "noisy pixel" was minimised by going together with adiacent ones who were less noisy).

And then again, you can repeat if the need be.
This is not a "perfect" solution, you cannot reduce the image too much (6000x4000 -> 3000 -> 1500 -> 750x500), but in certain cases you can save an image to be usefull even to a very low resolution.
As for web or a tablet, where an 750x500 is still an usable size.

Also you have to consider that the noise usually means that some pixels do amplify different then the adiacent ones. For less performant sensors, with higher amplification (high ASA / ISO) you can have all pixels with noise, in such cases you do not get a noise reduction applying this procedure, is that the colors and luminosity are just wrong for every pixel.

As you may observed from marketing and specifications, for a sensor size and same technology (let say same year ), lower the resolution is lowering the noise for higher ASA / ISO.
The same "technique" applied directly inside camera.

This is why I enjoy that NX1 has a pretty high resolution, 28Mpix, doing some "disco" photo without speedlight has allow me to have acceptable photos at arown 6Mpix for my client - my daughter.
Also I have used LR to minimize noise and compensate exposure and saved the export at 100% quality.
The REAL drawback is that with these very dark images, you cannot check instantly what is the result, you see nothing on display if you review the shot.
And best to record only RAW, the jpegs will be just black images...

6MP vs 28 MP doesn't change the noise much at the same image size.  People tend to think 28 MP camera would be noisier as they zoom into the image much more (enlarge it more) at the pixel level, so it appears noisier, but you are zoomed in more.

Noise should always be compared at the same output size.  Like take the 6 MP and the 28 MP image and print your 13x19 image or maybe resize to view on a 4k TV, etc.  The higher MP image will likely look better if dealt with properly.

As others say, in low light without a tripod, if you want higher shutter speeds you need more light in the camera.  The only way to do that is with a larger aperture lens.  This has trade-offs.  You get shallower depth of field at larger apertures, generally the lens won't be as sharp, you get more vignetting/darkening of the corners, etc.