Way back when, when he first joined a Netanyahu government, Lapid spoke a lot about this and while he was not able to keep Netanyahu down to the number 18, he did keep it in the very low 20s (23, if my poor memory serves me today). This past year when Lapid was a central member of the formed government, the number of minister ballooned insanely to keep everyone happy in this hodgepodge of parties.

In an attempt to make Lapid uncomfortable, MK Ophir Katz (Likud) has proposed a law that would limit the number of ministers to be appointed in any government to a maximum of 19 ministerial positions and an additional 4 deputy minister positions. As of right now, the law allows the Prime Minister to appoint unlimited numbers of ministers for his political needs. 

Katz says this law will save the taxpayer, via the Israeli government, hundreds of millions of shekels, and will also make the government more efficient. Katz says having so many ministers makes the government inefficient and adds much beauracracy and redundancy, making it more difficult for the average citizen to get the services he needs.

source: Israel Hayom

I like this proposal but know it wont pass, due to its coming from the Opposition. As much as it messes with Lapid, it also messes with the Likud and would make things difficult for them in the future in forming any future government.