In that case, how about if you tell us, to the best of your recollection, what this crane was like?
Let's start with the truck. Since you specified 15 tonnes, I figure that it has to be a dedicated drivable crane as opposed to a truck with a crane attached. (I very well might be wrong about that, but I personally have never seen an on-deck truck crane that could handle more than about 5 tonnes.) So, did it happen to have 2 dually axles on the back and 1 mono steering axle up front, with tires about 1 metre in diameter? If so, it was a mobile crane as opposed to a truck.
Now, describe the boom as best you can. How many segments? Cable for the last stage, or a hook directly attached to the last segment?
Anything else that you can think of to describe it will help. I have a suggestion in that regard. Google "mobile cranes" and go to "images". If you see something that looks like what you want to know about, click on it and then capture the image. Post it, or a link to it, here and then we'll know exactly what you mean.