Iran's economic strength is a threat to Israel now, their nuclear abilities might be a minor threat several years down the road. Even the most extreme Iranian regime would not use nuclear weapons preemptively. Without sanctions, Iran's economy was becoming a regional powerhouse, growing much faster than Israel's or any of its other rivals.
U.S. Defense Secretary Carter: Russia escalating Syria war by targeting moderates (Reuters)
from the article: Iran's Khamenei: West won't lift sanctions if Tehran drops nuclear bid