This is a good question,* because it highlights a common misconception that many Jews in the diaspora (and non-Jews, come to that) have about Israelis.
With the exception of old-timers from Eastern Europe and the Ashkenazi ultra-Orthodox communities (who regard Hebrew as being suited for prayer and religious study rather than for everyday conversation), the vast majority of Israelis do not understand Yiddish, nor use Yiddish terms.
Israelis of North African or Middle Eastern origin (roughly half of the Jewish population) never encountered Yiddish at all until their arrival in Israel (their immigrant parents or grandparents spoke either Arabic or Ladino), and virtually all Israelis of Ashkenazi background are also ignorant of it because their immigrant parents, grandparents or great-grandparents were actively discouraged by the authorities and by the educational system, on ideological grounds, to renounce Yiddish (and other foreign languages) in favour of Hebrew.
Consequently, terms such as yahrzeit (and, for that matter, shul) are utterly foreign and even somewhat alienating to Israelis. (The word Shabbes is known—but not in a good way—from frequent demonstrations of Orthodox Jews against violations of the Sabbath by the secular Jewish public.)
The preferred term for yahrzeit in Hebrew is yom hashanah יום השנה (lit., “the day of the year”), or azkarah אזכרה (in the general sense of a “day of remembrance”).
Oh, and shul, by the way, is beit-knesset. If there’s one word that Israelis would appreciate non-Israelis to say in Hebrew instead of English, it’s that one…
* with thanks to Chanah Caplan for asking.