Everything is negotiable.
Technically the 2015 MFs should have been paid by now.
I would expect to pay all 2016 fees. The buyer may have paid these, if they are up to date, however they could pay by the month.
What is the UY?
Do the banked 2015 points expire soon? (Like an april UY?) Remember ROFR and closing will take time. Those bank points might have limited life on them, depending on UY.
I would offer to pay the 2016 Fees, not the 2015.
See if they accept.
I MIGHT pay 2015 IF it is a late UY, and then only on the portion of points that you get.
If the seller banked all 2015 points, it is in many ways like you are purchasing the contract a year ago yourself, and banking the points yourself, so you would have paid the MFs. But again, assume at least 2 months before you can touch any points, so that could distress the banked points, reducing their value.
I just bought a contract, August UY, with no 2015 points, and offered to pay prorated MFs (August on), buyer rejected. From my point of view, if I were buying Direct,with an August UY, I would only pay MFs for August on, not all of 2016 (unless Disney got me 2015 points as well, and then paying all 2016 MFs would be fairl) But the Price per point was good enough that I caved.