Thank you for providing the information there, Marc. The first thing that jumps out at me is that you are running a 3rd gen i5 with only 8gigs of system ram. The Intel i5 processor, with the exception of the i5-4570T, are all quad-core processors. When you are rendering you are using only 4 cores to create the image. Granted you have a good clock speed @ 3.10 ghz, but you would still be rendering much slower than someone who has a Core i7 @ 2.8ghtz because they are using double the amount of cores to render. Also you have a very early generation processor which is not very efficient compared to more recent generation of Intel processors, even at slower clock speeds. Your 8gb of DDR3 system ram may not impact rendering directly, but certainly does create some bottleneck in data transfer on the system compared to newer, faster DDR4.

The NVidia GeForce GT620 has only 96 CUDA cores running at 700mhz. This card, of course is very slow compared to even a low end GTX card which could have over 1000 more cores than what you currently have. In fact, it's not doing very much to help your i5 render a scene, if it's being used at all. When you compare the number of CUDA cores in your GT620 to a GTX 1060, you can see there is an insane performance difference there. Here's a benchmark comparison:

http://gpu.userbenchmark.com/Compare/Nvidia-GTX-1060-6GB-vs-Nvidia-GeForce-GT-620/3639vsm8899

Your current card does not even register on most of the tests, so an upgrade would absolutely help you with what you want. The only thing is you have got to make sure you have the available slots to put this new card in, because it is much larger than your current card, and requires a lot more power. Your current machine is not quite up to the standards of the average machine I see using these new generation GTX cards, and I'm not sure your board or your power supply will hold up.

In all honesty, I would recommend waiting and saving some money to purchase a new machine down the road. AMD are coming out with their new line of processors now (Threadripper and Ryzen), and Intel are introducing the i9 soon, so the cost of later generation i7 processors will come WAY down very quickly when that happens. A processor upgrade will help your render times immensely. I also recommend no less than 16gb of ram for doing almost any kind of graphics intensive work, but that's another story.

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