GAZA/JERUSALEM (Reuters) - Israeli shelling killed at least 15 Palestinians sheltering in a U.N.-run school and a**ther 17 near a street market on Wednesday, Gaza's Health Ministry said, with ** ceasefire in sight after more than three weeks of fighting. Israel's security cabinet convened to discuss a revamped Egyptian proposal for a truce but it was unclear whether any decision was imminent that could halt a 23-day conflict in which nearly 1,400 people, mostly civilians, have died