MADISON - Fifteen people have died from snowmobile activities this winter in Wisconsin. That's five more than a year ago. Department of Natural Resources officials say speed, alcohol and nighttime driving are among contributing factors. They also say increased snow may have contributed in some cases. They're warning sledders to take extra care as spring nears and ice thins on lakes and rivers. The DNR also urges snowmobilers to take a look at their website for more safety tips.