Mahindra XUV 3XO

Since your running isn't high - only around 6,000km a year - it would make sense for you to opt for the petrol. 

The higher purchase price of the diesel won't be justified given your usage. For reference, the Mahindra XUV 3XO AX7L for the petrol-manual variant costs Rs 12.75 lakh and Rs 13.43 lakh for the diesel-manual (ex-showroom), and the price delta will only be greater when it comes to on-road prices.  

Of your three shortlisted cars, the Mahindra XUV 3XO checks the most boxes. It has a very spacious cabin - although not a very spacious boot - and has a comfortable ride and loads of features. 

As for longevity, any car can be kept for 10+ years if you drive it carefully, maintain it well and have it serviced regularly. That said, Mahindra's aftersales and service isn't as well-regarded as, say, Maruti or Hyundai's, so that's something to keep in mind. 

You should also consider the newly launched Hyundai Venue, which also meets all your requirements very well, and comes with more modern tech inside the cabin.

All the compact SUV options you've listed are powered by turbo-petrol engines, and since you are looking for efficiency, be warned, in typical city driving (stop-go conditions), these turbo-petrol engines aren't likely to be very efficient. 

Also, these are very sensitive to the driving style and ambient conditions, which can drop the mileage down to single digits. Among the options you've listed, the Mahindra XUV3XO 1.2 Turbo (MPI) AT is likely to satiate your need for performance while offering a smoother and comfortable experience overall. 

Another option you may consider is the Citroen Basalt X/Aircross X, provided there is a Citroen touchpoint in your city. However, if you want to keep the running costs down at all costs without sacrificing performance, go for the Tata Nexon EV 45.

While the Tata Sierra is an impressive-looking SUV, we have yet to drive it on the road and experience its performance. 

Also, the price list for all the variants is not out yet, so it’s uncertain which variant will be available within your ₹15 lakh budget.

Tata's after-sales and service support does have some catching up to do in comparison to Maruti and Hyundai. If you really liked the way the Sierra looks and what it offers, it would be worth waiting for. 

However, if it does not turn out as per your requirements, the Mahindra XUV 3XO in AX5 L variant is very good. It has a smooth powertrain and a good feature list, along with a spacious rear seat and low maintenance costs. 

The Kia Sonet diesel is a good option, and you can safely go ahead with this.

However, if rear space is important to you, then you will find this very tight in the Sonet, especially so in comparison to your Toyota Glanza. If this is an issue for you, then you could consider the new Hyundai Venue; rear space is better, and on the whole, the car is a better option too. 

However, if you are not keen on the Venue, then you could consider the Mahindra 3XO, which has good space as well as offers a good ride along with engine performance.  

Since your usage isn't particularly high, a petrol automatic would make sense. Not only will it be more refined than a diesel, but also be more affordable to purchase. Within your budget, there are plenty of options, with naturally aspirated and turbocharged engines and CVT, DCT, AMT and torque converter automatic gearbox options.  

If you want a well-rounded SUV, the Mahindra XUV 3XO is the one to go for. It's got a spacious cabin, it comes loaded with features, and there are two petrol options as well. However, if you enjoy driving, you'll find good value in the Skoda Kylaq.