I have a 15-year old Japanes Maple (not sure of the variety - it had lost it's tag and was only $15 while other trees were #75!) whose leaves are turning red too early and falling off. I know this is usually a sign of water stress, but this tree is quite big (15 feet tall) and we have had abundant amounts of rain this summer in the northeast. What else could be happening? Is it dying?

Thanks.