The build of the project in Android Studio slows down, what should I do?

Question

linux

Installed AS on Debian 8.1 32bit the other day . The studio started up quickly, I created a test project and clicked on the application launch button, to which the studio responded with a device selection dialog box in a couple of seconds . I chose the emulator, and then I got an error saying that the emulator does not work well on 32-bit systems.
I thought that for the sake of AS I was ready to reinstall the system. Now I have Debian 8.1 64bit . The emulator is running. But another problem appeared: the application takes a very long time to build (the "Gruble Build Running" hangs).
Tried deleting AS and SDK and reinstalling - doesn't help.
What could be the reason for the hang when building the project and what to do about it?
UPD:
The following task hangs
Executing tasks: [:app:compileDebugSources, :app:compileDebugAndroidTestSources]

Answer 1

The problem was solved by rolling back Build-Tools to version 21.1.2. What exactly was the problem - I did not find out.

Answer 2

I use Eclipse and had a similar problem until I increased the amount of memory in the ini file.
Directly on the emulator, if you use an x86 image instead of ARM, then it is emulated much faster.

Answer 3

Look in the Gradle Console, are there any errors?
If there is something like "...timed out while wating for slave aapt process..." then you need to install some libraries for i386 architecture:
dpkg --add-architecture i386
apt-get install libncurses5:i386 libstdc++6 :i386 zlib1g:i386