The sensor of the Panasonic Lumix DMC-LX15 is 2.74 times larger than the sensor of the Panasonic Lumix DMC-LX7. That's a big advantage.
If two sensors use the same technology, a 2.8X sensor would almost be the same as the other two stops Advantage in terms of signal-to-noise ratio (SNR or S / N ratio). By comparison, full-screen sensors are about 1.5 times larger than APS-C sensors and thus enjoy an approximate rating a stop Difference if both use the same technology.
The pixels of the LX15 are slightly larger than the pixels of the LX7. This means that the LX15 is 2.74X as large as the LX15 compared to the 10X LX7. While megapixels are not the nuts and bolts of what some people make out, more megapixels allow for larger display sizes before a picture appears pixelated.
The LX15's 24-72mm (35mm equivalent) f / 1.4-2.8 lens compares pretty well with the LX7's 24-90mm (35mm equivalent) f / 1.4-2.3 lens. It is not zoomed out so far and it is one little At 72 mm (35 mm equivalent) slower than the older camera, it is 90 mm (35 mm equivalent), but only about two-thirds of a stop.
Combine the differences between the sensor sizes and the maximum aperture sizes of the two cameras. The newer LX15 has one 35 mm equivalent opening¹ of f / 3.8-7.6 compared to LX7 with a 35 mm equivalent opening¹ of f / 6.4-10.6. This means that at 24 mm (equivalent to 35 mm) you can expect a performance advantage of around four-thirds and at 72 mm (equivalent to 35 mm) with the LX15 compared to the LX7 an approximate stop.
In other words, in terms of low light performance, the LX15 is similar to the LX7 like an FF camera with an APS-C camera. That's a big difference in low light.
This is also true before taking into account the potential impact of the four-year technological difference between the LX7 published in 2012 and the LX15 published in 2016. This can be a big factor as the sensor technology improvement has increased a bit. In general, comparable models between 2008 and 2012 are expected to show more improvement between 2012 and 2016 than comparable models. But every case is different.
As far as the price differences are concerned, the cheapest FF cameras are at least twice as high as the cheapest APS-C cameras. The Canon EOS 6D Mark II is offered for $ 1,800, but currently sells for about $ 1,300 at an immediate $ 500 discount in the United States. The Canon EOS 77D lists for $ 750 and costs about $ 700. (The 77D is quite similar in terms of features and controls to the 6D Mark II, both introduced in 2017, both have similar 45-point AF systems, etc.) Rebel / xx0D models can be cheaper, but they do not the same level of controls and other functions.)
Is securing the future a big factor here?
There is no proofing for the future, especially when it comes to cameras. When a model comes on the market, the replacement for this model is already anticipated by many camera-driven gearboxes before photography.
¹ Equivalent aperture (in 135 film terms) is calculated by multiplying the lens aperture by the crop factor (a.k.a., focal length multiplier).