I don't have the 1500 but I do have the 2500 and the ATPro. I did a comparison last week at a playground. There is an 8 sided swing set (8 individual swings on a circular frame). I started out with the GTI 2500 and did a good search around all the swings, both inside and outside of the circle. I retrieved 14 coins (clad). I made another pass with the GTi 2500 and picked up 3 coins that I had missed. I didn't dig the signals that showed that is was larger than a coin, or anything less than a 7 which meant no nickles.
The AtPro was next, I set it on Promode and custom eliminating anything below an 80. Maybe something is wrong with my 2500, I don't know, but I went around the swing set with the AtPro I picked up 10 more coins. I then reset the ATPro to zero mode, disc to 36 with Iron Audio on.
I made another pass around the swing set and picked up 4 more coins (2 nickels).
This took up most of the morning and I left for the day.
I think that now that I am very familiar with the ATPro, and haven't used the 2500 much since I got the ATPro is the reason the ATPro did better.
The ATPro is my first choice when clads abound, but I think its all about which machine you are the most familiar with and the one you have the most confidence in.
Roy