I've been in a group that went to 30k so I can understand it, the person may be in a group where they've battled against someone they know goes high, in a big spender group 1500 difference is nothing to surpass, boosts are half price, if they are still trying to get trio animal or something they need, boosting while they try is just smart. 15 gems is nothing to boost if you're speed breeding anyway why not? We don't know what their game play is so I'm not going to judge