MacBook Pro fan runs loud constantly and battery draining within a couple of hours

Start by reading If your Mac battery runs out of charge quickly - Apple Support.

That Support document is very superficial though. Read it, then follow up with About fans and fan noise in your Apple product - Apple Support. It too is fairly superficial, but if you persist in reading the links within it, it will eventually lead you to View energy consumption in Activity Monitor on Mac - Apple Support.

A previous version of Learn more about the operating temperature of Apple laptop computers contained this most relevant excerpt:

"If your Mac laptop gets warm even when it isn’t doing tasks that require intensive calculations, or if it has fans that run for a long time, use Activity Monitor to check CPU activity. Look for malfunctioning processes that can put a significant load on the CPU and check for unexpected fan use. If issues persist, close and open the lid on your laptop, or restart your computer. If you have an Intel-based Mac, reset the SMC."

Using View energy consumption in Activity Monitor on Mac - Apple Support, select its View menu > My Processes as a starting point. Sorting that list by %CPU in descending order will reveal the most demanding processes. One or more are likely to stand out as particularly burdensome.

Post a screenshot of that Activity Monitor window if you wish.

Since yours is an Intel-based Mac, resetting the SMC may be all that's necessary to restore your Mac's normal behavior: Reset the SMC of your Mac - Apple Support. Just be sure to exhaust all the other possibilities first.

MacBook Pro 15 2015 i7 16GB often got hot and made noise, tried cleaning it, updating thermal paste, resetting the SMC, reinstalling the OS, disabling animation, switching to the old Catalina OS, cleaning startup... there was 0 effect.

Here's what helped:

1. Install the free application "Turbo Boost Switcher" and click on the "Disable Turbo Boost" function.
2. Install the free application "Macs Fan Control" and configure both fans in it - "Sensor-based" in a temperature mode of 60°C and 90°C. The first fan was installed on the CPU Proximity, the second on the Intel Iris Pro GPU (or whichever one you have).

After this, the fan noise disappeared. The temperature is not rising. Productivity has not decreased. I ran high-load tests with these parameters and they all passed successfully.

It feels like I bought a new Mac.