Are you trying to upload from the Pilz device, or from the PLC ?
I do not think you can upload from the Pilz device itself into TIA.
The S7-1500 hardware configuration incl. safety should be possible to upload, provided it was made with TIA 14SP1 or greater, and it was released to upload in the safety configuration. See chapter 2.5 in this manual:
https://cache.industry.siemens.com/...5_Programming-Guideline-Safety_DOC_V10_en.pdf
I am also guessing you will have to provide the password for the safety program.
Disclaimer: I dont actually have experience uploading from a safety S7 PLC.
Not sure if it has changed or not, but I remember trying to upload from an safe PLC (1515-F) but it wouldn't let me due to an option that needs to be set when downloading.
I don't have an safe PLC with me now but will try to do some testing later. I haven't used V15 much yet. Maybe it has been fixed.