Problems to reinstall Photoshop 15

I apologize for mistakes in this post but I am using a translator and I hope you understand the meaning of my request.
had to reinstall Photoshop 15 (regularly registered on the Adobe server) on my PC after which, for various problems, I had to reinstall Windows professional again. The installation was successful but when I try to open the installed program, after entering the serial number and accepting the contract, I get the message "Could not validate the serial number." I have already contacted Adobe who informed me that , being the version of Photoshop 15 of 2016, the activation servers are no longer available and for this reason the error is detected when I insert the code. You can help me since the specialized research licensing team that directed me to this forum:Alright, as I was able to review this is correct serial key, please try again, also I would like to inform you that as you are using older versions of the Photoshop Elements and the support for the older versions has been discontinued from our Adobe chat and Phone support, but still available on our Adobe forums, which is forums.adobe.com please refer to this article and post your query.