All games stuttering, even old ones

Without proper diagnostics, there is very little anyone can do aside from wild guesses and "Did you already try ...?".

That being said, here are some pointers that may help you find the correct solution:

• Your assertion that CCleaner is in any way related to performance is false. It doesn't increase performance at all.
• The MX 150 is a notebook graphics card, and was not designed for good performance, but rather for delivering acceptable performance with low impact on heat and power usage. Because most people don't play GTA V on a laptop with a low-end GPU.
• Speaking of heat, notebooks are known for having terrible heat conductivity. Try installing an application like MSI Afterburner and measure the temperature. It might be that your GPU is at something like 85°C and to avoid overheating, it throtles down to preserve itself.

The problem can come from various sources: GPU driver, CPU stutter, dying HDD, general overheating problem, etc.

GPU

You should first ensure that you have the latest drivers for your GPU. In either case, a clean reinstall might solve the problem, be sure to select the "clean install" checkbox to remove the previous driver's configuration. If that doesn't solve your problem, you can also try doing that with an older driver.

CPU

Sometimes Intel's TurboBoost can cause stuttering, so you can try to set the maximum CPU speed in your power management settings to 99% instead of 100%, which will prevent TurboBoost from kicking in. Just go to the Control Panel > Power options > [your current battery plan] Change plan settings > Change advanced power settings, then in the list find Processor power management > Maximum processor state and set both values to 99%.

Overheating

Appart from TurboBoost, your computer can also overheat from dust build up, so it's a good thing to clean it up every once in a while. If you can open it, you're golden. Just grab a can of compressed air and blow on your fans/heatsink to ensure the airflow is unobstructed (you'll find videos on how to do it on youtube if you're afraid of breaking something). A simple straw might work too, just be careful not to spit in your computer by accident. If you cannot get it open, try to blow air through the vents and openings to get most of the dust out.

Of course, check if your warranty is still valid before opening it, as doing so may void it.

HDD

FPS loss can also happen when your hard disk is under too much pressure or dying (downloading/installing game updates in the background can be too much in some cases, thanks Steam!) Since the disk usage doesn't seem to be that high in your case, it means that your hard disk might be failing. In that case, back up your data as soon as possible and replace the hard disk.