How do I prevent Google Search from spawning instances?
From my own experience of Lollipop, it's Google's new concept to show you everything you're doing as a separate activity. Unless you go down the route of rooting and applying some mod (I don't know of one which does this), the only solution I see is to get into the habit of always closing them as soon as you open them. (Easier said than done, I can say for sure).