Early relieving from company

Hi All, I am working as an IT professional in a company. Current company has 45 days notice policy before leaving. I have resigned from current company few days back. I have told my new employer of 45 days notice period policy in my current company and has also told them that I can try to negotiate with my current company to cut down the notice period to 30 days. My new company want me to join even before 30 days and is ready to buy out 30 days of my notice period in current company. But my current company has denied to relieve me earlier. They are saying they can relieve me atmost 15 days earlier with 15 days buy out amount. What should I do now?