Suppose you are in a hot air balloon with a sandbag that has a certain mass. The hot air balloon is moving upwards at a constant velocity of $15$ $m$.$s^{-1}$. If you throw the sandbag out of the hot air balloon, will the velocity of the hot air balloon change?

I thought that it will increase, because according to Newton's first law, an object will move in uniform motion unless an unbalanced force acts upon it. If the sandbag is released, there will be an unbalanced force. Or am I wrong? Please help.