Upgrade for ORD to CDG

Hey guys, planning on getting two one ways from ORD to CDG for my wife and I at the end of May 2018. She will be doing a masters program there for two months and we plan to travel around after that so not sure when we will fly back. Anyways, I see there's availability for 25k points in economy and 62.5k in business on Air France. I was looking around on their site and it says that I could upgrade with points after reserving a ticket to premium economy for 7.5k or 15k for business. Does this mean business would then only end up being 40k, am I understanding this correctly? Also, has anyone paid to upgrade and if so, how much?

If it helps, we currently have a combined 100k UR and 70k AA but planning on getting CSP for both of us soon to get additional 108k UR.

Thanks for the help!