WordPress takes too much time (100 seconds) to load – Front end and back end

You should not ignore those warnings.
From screenshot, It shows your theme is using deprecated mysql functions.
Check your apache2 logs -> If this is really an issue there will ton of logging
If yes, your theme is causing the issue.

If the above is true, do this:

1) Switch to some other theme.

2) Remove the parent theme code. (instead of just disabling it)

3)Upload the latest version of theme.(I am
Assuming the update for that theme is available)

Let me know if that works.