How and when to descend?

This is a non-pilot here, so bear with me when you read this...

On a Career Cargo flight in a Pilatus PC-12 at 36k feet (or something like that) on the final leg of my cargo journey, ATC asks that I descend to 15k, so I do. However, the instructions tell me to "enter the pattern," but I get no more instructions from ATC. The pattern is certainly not at 15k feet. It's more like 3k feet. I, sort of, waited for ATC to ask me to descend more, but they got real quiet.

Question: When and how to I descend from the 15k? Do I just reach it and keep going? I can certainly just do whatever I want, but I was trying to do it right.

As always, thanks for the expert assitance. It is appreciated.