It seems like alot.
I only had a couple of airplanes that needed tail weight and both only needed a small amount.
1 was a Cessna and that makes some sense because of the short tail, the other was a Hobbico Brightstar and that took less than an ounce.
Most airplanes can either be balanced by moving the battery around or need nose weight.
Long answer to maybe its too much?
Are you sure you measured right?
The farther back you put the weight the less you will need.