Don't fall into the trap of thinking that because it's a group gift, it has to be something obvious and boring. The money is there - what's missing is creativity.
With $15 per person, you can pool together a decent amount if there are several of you. The best approach is to go for something they'll actually use or enjoy: a bottle of good coffee or tea if you know they like it, a set of small tools if they're the type to fix things around the house, a book about a topic they're passionate about, decent wireless earbuds, or even an experience (movie tickets, a restaurant, an activity they've mentioned wanting to try). If your boss is into sports or travel, a compact travel bag or a travel accessories kit tends to be useful without being generic.
The important thing is to ask around beforehand if anyone knows what they're actually interested in. Don't assume. And if you have no idea what their tastes are, better go for something practical and good quality that they'll use anyway, rather than something flashy that ends up in a drawer. A group gift works better when it shows you put some thought into it, not just that you had a budget.