SYDNEY (Reuters) - Australia s Bureau of Statistics said on Tuesday 9.2 million people, or 57.5 percent of eligible voters, have cast their votes in a ballot on whether same-sex marriage should be legalized. Australians began voting last month in the non-binding poll, conducted by post, to inform the government on whether voters wanted Australia to become the 25th nation to permit same-sex marriage. The results of the poll will be declared on Nov. 15. The first official update suggests a high turnout is likely despite the ballot being non-compulsory. Turnout levels will go a long way in determining whether Australian Prime Minister Malcolm Turnbull can finally resolve a topic that has dogged his tenure as leader and threatened to split his centre-right government along ideological grounds. Low turnout would have seen the issue continue to dominate the political discourse whatever the result, underpinned by  questions of legitimacy in a country used to compulsory voting. The first official update on the progress of the same-sex marriage survey comes just a day after a Sky News ReachTel poll showed the  yes  vote on track for a comprehensive victory. More than 64 percent of those surveyed have sent back their ballot and voted  yes , the poll showed, with a further six percent planning to support same-sex marriage.   A widespread victory may do little, however, to heal a divided the nation of 24 million people, which has split along religious and generational lines and at times has threatened to turn nasty, prompting parliament to strengthen laws preventing hate-speech. 