Lollipop - disable certain background process

I have an old (but rooted) phone running Android 5.1.1 (Lollipop). I realized it runs many background processes which I absolutely don't need. I can stop them manually via Settings > Apps > Background processes, however I wish to keep them disabled: they slow down the cold-start of the phone which I don't like. So I'm looking for a way to not just disable but completely ban certain processes (i.e. ban them from starting). How can I do this on these old versions of Android? Unfortunately Google is quite blurry and noisy for these search terms.