so I've finished making a full fledged Android application with which I store data and retrieve on Firebase Database.
However, since there are many joining statements (By using orderByChild and equalTo), the main home screen is very laggy.
The main reason why I'm using Firebase, is because it is a real-time database, however, there is only one screen where that is useful.
Do you think that it's a good idea to keep most of the data on an SQL database and only the data that requires real-time data transfers on Firebase, and will using SQL databases reduce the time it takes to load my home screen?
If you have a SQL background and you want to rewrite your application to use only Firebase, to have a better understanding, please take a look at this tutorial, The Firebase Database For SQL Developers. I asure you, Firebase will handle all your needs.
If don't have time to do this, than use Firebase just for the single activity that you need. If you think that in the future you'll need to make more than one section of your app to use Firebase, than think to change the whole app to use only Firebase.
Hope it helps.