7
About 50% of the US fleet of F-35s (A/B/C) is incapable of conducting combat missions.
(www.gao.gov)
I don't see where you're getting that 85% number. Appendix III of the PDF has the data. The numbers don't look good to me (I don't know what would be considered a "normal" capability rate for military aircraft) but they're generally much higher than "15% capable", especially the newer subset of aircraft.
What's more disturbing to me from the PDF is "DOD plans to procure nearly 2,500 F-35s at an estimated life cycle cost of the program exceeding $1.7 trillion. Of this amount, $1.3 trillion are associated with operating and sustaining the aircraft." Those are our taxes (plus vast sums of supposedly "unsustainable" debt), being funneled into the pockets of the MIC and ultimately into the pockets of the wealthy elite, rather than being spent on critical domestic social needs (Medicare/Medicaid/Social Security for ex.) or just being left with the taxpayer.