Don't forget Israeli aircraft have to fly over 1000 kilometers to get there. Russia wants to hit them before the reach Iran. Not to mention the reception party waiting for them in Iran. It's going to be a "slam dunk" as some neo-con/Zionists described it some time ago referring to invasion of Iraq.
U.S., allies conduct 1 air strike in Syria and 11 in Iraq against ISIS militants (Reuters)
from the article: Russia to begin loading fuel into Iran's nuclear reactor next week