Time has come to change tyres. People often upgrade tyres. I decided to downgrade to 15". For those interested, Here is how I went about it.
BTW. Easier way is to find 15" alloy and plonk in the tyres. I wanted steel rims, hence, some work has to be done. Without further ado. Here goes.

15"steel rims on 215-75 R15, 16" alloys on 215-65 R16.

Here is a front view on how they stack up. The difference should not be so dramatic if the old 16" tyre was not so worn out. The wheel wrench is there to prevent the tyre from rolling.
The 15" steel rims are sourced from Mahindra Scorpio new model with 114.3 PCD, at least that's what the tyre shop told me. People upgrade their tyres to alloys and they dispose the old ones, and those are the ones I got for INR 1000 each. As mentioned earlier. Get alloys if you don't want to go through the hassles I went though as described it below.
NOTE to anyone thinking the same route I took. Mahindra has different steel rims, same size, same PCD, and looks almost identical. Maybe from KUV, Scorpio etc. I did try the KUV ones, It did fit the Duster, but I could not tighten the nuts completely, as the duster nuts were wee bit too long. With the Scorpio rims, I did not have the nuts issue but had some other issues as you will see below. No doubt KUV rims will also face same issue.
I fitted the Scorpio rims on the front. It fitted perfectly. I was elated, only for a moment, as I found out, the rims were pushing against the brake callipers. and the car was struggling to move.
So I went to the lath machine workshop and have the made this for me.
Wheel spacers, They are 3mm thick, I figured they should suffice. Made two of the, just for the front. The rear has no issues.
I fitted all tyres, all seems fine and was heading back home when I noticed some scraping noise. I knew the rims were scraping against the callipers again, but the noise was not so bad, besides the car was moving effortlessly, so I just went ahead. The noise eventually died before I reached home. Anyway I thought I would look into it. And here's what I found out and did to solve the problem.

Left callipers. Notice the scratches. They were not more than scraping the paint off.

Left rim. Notice the scratches. I ran my hand over it, they were no more than scratching the paint.

Right callipers, The scratch on the right were more than the left. But we are talking in fraction of mm.

Right rims. The scratch here also were higher than on the left. I ran my fingers over them but could barely notice any deformation.
As I already mentioned, the scraping noise disappeared before I reached home. Anyway, I decided to make sure the never come into contact again.
I took out my angle grinder and grind off the callipers on both side (see pics above circled in RED). Don't worry the grinding here is in paper thin depth, so structural integrity of the callipers should not be compromised.

Finally, here is how it looks.

Here is another view to get an idea on the Off-set of the steel rims.
Had driven some since then. All seems fine. Ride quality over bumpy road has noticeably improved. Tyre noise of the new A/T tyres cannot be ascertain yet as I have not had the opportunity to push the car on a decent stretch of good paved road

. But this is precisely why I am going for A/T tyres with higher side walls. Cheers.