Unity Android App size too large

Hi guys,
i'm a newbie and this is my very first approach with unity, i'm just experimenting something, so in my project i have only 2 scenes, every scene with 1 camera, 1 canvas, 1 panel and some text (so no sprite, no light, no effects, nothing)...

Problem is when i build the project apk is 17mb and when installed on phone it explodes to 65mb...
Strange thing since my app does almost nothing...
I think it should be far less heavy than 17-65mb... or am i wrong?
Hope you guys can help me

Some further informations;

1. I'm on Unity version 2017.2.0f3 Personal (someone said me that PRO version could reduce app size, is it true? and if yes, how much?)
2. In the "editor log" i can see that the complete size is 4.6 mb
3. In player settings i'm using only arm-v7 as device filter and .NET 2.0 subset
4. I'm using gradle and IL2CPP to build
5. I'm in 2d project
6. I noticed that the heaviest files in the apk produced by unity build (says the installer of the android application) are .so files in armeabi-v7a... about 45mb (when i export the project to open it with android studio those files are about 200mb!)

EDIT: i just noticed that the file taking the most of the space is libunity.so that weight 35mb before installation on phone and (i think) about 50-60mb once installed...
Do you have any ideas about how to reduce this file size?

EDIT 2: Just for completeness

Code (CSharp):

1. Build Report
2. Uncompressed usage by category:
3. Textures      37.7 kb     0.8%
4. Meshes        0.0 kb     0.0%
5. Animations    0.0 kb     0.0%
6. Sounds        0.0 kb     0.0%
7. Shaders       0.0 kb     0.0%
8. Other Assets  4.8 kb     0.1%
9. Levels        45.2 kb     1.0%
10. Scripts       615.3 kb     13.0%
11. Included DLLs 3.9 mb     84.8%
12. File headers  17.1 kb     0.4%
13. Complete size 4.6 mb     100.0%

EDIT 3: Just made an empty project (no objects added, no scenes, nothing... same player settings) and having same data size, it seems the real problem are .so files, just don't know how to reduce them

 

Due to lack of response i decided to change framework and pass to phonegap or react native.

 

Using Unity Pro does reduce size, but (for me it's not worth it so I do not know the size reduced). What Unity Pro offers is that it removes the Unity loading screen which should release a few megabytes.