Don't worry about the medicals now.
If they process your application with 15 months from the day when you did your medicals. After the process completion, if the decision is a positive one than they will internally extend the medicals and just give you VISAs. From the looks of your case.....your marriage equinity is good that's why the status changed to In Process so now as long as nothing alarming happens during background checks. You most likely won't have to do re-medicals EVEN if it expires. They will re-new it for you.
Hope this helps.