score:4
In general in the US, the 15% guideline only applies if you're getting some service associated with your food/beverage - service in a sit-down restaurant, food delivered, etc.
If I'm getting coffee to go and paying cash, I'll usually throw some of the coins I get in change into the tip jar, but that's as much because I don't like carrying coins as anything else. (The largest commonly used coin in the US is only worth $0.25.) If I'm paying with a card and presented with those options, I'd skip the tip.