Burning Hands goes 15 feet these days?A low AC wizard trying the new tactic of running up to within 15 feet of a troll and making it angry? The people I play with are smarter than that.
In my game it only goes three, meaning that to cast it on a Troll you're going to be well within its reach.
Good luck with that. Please make sure your Wizard's will is up to date before attempting.