What if I don't want to upgrade to marshmallow?
Will my phone continue harassing me endlessly to do so?
Yep.... it will unless you root and modify some system stuff to eliminate the check.
Why, might I ask, are you refusing to take the upgrade to marshmallow?
Because I got marshmallow on my moto g 3rd gen and now I can't connect wifi at work and I'm seriously pissed. And when i got lollipop on my last phone, it was ****ed up as well. Thinking about reverting to an older model that won't constantly disappoint me.