I think you may have misunderstood, the F-15 deal is not a mid-life upgrade. The $2.4b F-15 equipment package is all the support equipment and electronics for South Korea’s potential purchase of 60 Silent Eagles , not an upgrade for their F-15K Slam Eagles. ROK are not looking to buy both F-35 and F-15, the competition is still on (and includes Typhoon, which I would think is a very unlikely contender), but I think they’re a way off a decision yet.
So, just to clarify, the two sales in the documents are:
60 conventional F-35As and associated support equipment for $10.8 billion (including ALL the stuff that SpazSinbad listed in Post #1630)
60 radars, DEWS, target pods, IRSTs, comms, parts, training and logistical support, etc. to equip 60 F-15Es (which are included in a separate deal) for $2.41 billion (not including the airframes). It has not been announced yet what the other part of that deal will cost.
The reason that notification of the potential sales has been made now is to save time later when ROK make their decision to buy ONE of the three contenders.