Yes, there is increase in performance compared to the single-channel and dual-channel RAM.
Good example is to compare the performance of RAMs, where only the DIMM amount is different. All the rest is same: RAM make & model, total RAM amount, RAM frequency and even Cas Latency;
Hard to say. Since you need to find the exact RAM that works in your laptop + taking laptop apart to change the RAM, without breaking anything else during the RAM switch. Also, you'd be wasting money for new set of RAM.
If you'd have desktop PC, where RAM change is far easier, i'd be more incline towards the RAM change. But for laptop, with high chance of braking something, i personally, probably, wouldn't do it.
Oh, if you are planning to buy 2nd 16GB RAM stick, to get dual-channel and increase the total RAM to 32GB then do note that getting both RAMs working has a 50:50 chance. For a guarantee of RAM actually working, buy a set of two sticks, since those have been tested by manufacturer to be working with each other. While individual sticks are trial-and-error, either they work with each other or not.
Is there difference? Yes.
Is it notable? No.
CL is Cas Latency, a time measured in clock cycles that defines how fast RAM can access data on it.
Though, the lower the CL is, the better (faster) the RAM is. E.g in my desktop PC, i have a RAM with CL15 @ 3000 Mhz.
The formula for it is: (Cas latency / RAM speed) x 2000 = latency in nanoseconds.
So, to put the numbers in there, we get;
(22 / 3200) x 2000 = 13.75 nanoseconds
(20 / 3200) x 2000 = 12.5 nanoseconds
(15 / 3000) x 2000 = 10 nanoseconds (<- my RAM, just for comparison)
With this, difference between CL22 and CL20 is 1.25 nanoseconds. Though, do note that 1000 nanoseconds = 1 second. So, the difference isn't noticeable, let alone notable.