The Israeli government is reportedly seeking to purchase an additional squadron of F-15 fighters, before agreeing to purchase any additional F-35 fighters:
The F-15 has the range and payload that the IDF needs, and that the F-35 stealth fighter lacks. It also is available today as a working, operational weapon. The F-35 is not.
As was enumerated in a recently released, internal report, the actual performance of the F-35 during combat exercises has been more mixed and less stellar than the sound bites offered to the press. At a recent Red Flag exercise, for example, the combat readiness rate of the F-35 was less than 25 percent:
Add to that the fact that the F-35 won't be able to use most of its air-to-ground weapons until the Block 3F software is available (which may not be until 2020 according to some reports), and it is obvious as to why the IDF is interested in more F-15s.
A better option still would have been if Israel still had its own fighter development capability, something that was killed when the Lavi program was canceled decades ago.