Unfortunately, you will only be able to use functions based on RGB video with your old second generation processor. Depth and IR will not work. There is no workaround for it. I'm very sorry.
Can i replace my current 2nd generation core i7 with Intel® Core™ i7-7740X X-series Processor?
It‘s too expensive for me to buy a new laptop so I am trying to see what I can do. I also like my current laptop. Will I also need to upgrade the DDR?
Laptops processors are usually not upgradable because the manufacturer fixes the processor the the circuit board (called the 'motherboard') with permanent solder instead of having the chip plugged into a socket like on desktop machines. Also, the motherboard usually has to have in-built compatibility with the chip replacement, so even if you could insert a new chip, it would not work with the PC motherboard.
If you were considering an X-series processor and DDR memory, it would probably be cheaper just to get a laptop with a 6th generation processor (the minimum for the SR300 camera). As 6th generation Skylake is approaching a few years old now, you may be able to pick up a good deal somewhere on a Skylake laptop. I myself use an Acer Aspire ES 15 laptop with Skylake processor as my main work machine.