This has been answered by Rickard
I'm afraid i don't know for sure if this decision was made within Sony or by Google but as i understand it, the global Equalizer was removed in Nexus as well and i also found this:
http://developer.android.com/reference/android/media/audiofx/Equalizer.html"NOTE: attaching an Equalizer to the global audio output mix by use of session 0 is deprecated."
Hi and welcome to the community!
As mentioned earlier, the equalizer is still available for 3:rd party apps but it's now up to the app developer if they want to use it or not. If the application you use doesn't use it i would recommend that you contact the developer of the app to see if it's something they can add.
It may be possible to downgrade the phone using 3:rd party tools but it's not something i would recommend and changing the phones software using 3:rd party tools may affect your warranty. If it's something that you still want to do i recommend that you check
http://talk.sonymobile.com/t5/Android-development/bd-p/22051http://talk.sonymobile.com/t5/Xperia-Z3-Z3-Dual/Equalizer-problem-after-lollipop-update/m-p/972944#M...
