the answer is easy, run at 100 Khz freq, and use more powerfull mosfet such as irfp460 and use big trafo core, such as ETD49 and above. while do primary and secondary winding avoid to use single cable even its big, and use parallel coil awg24 to awg29. Good and fast diode at output, 15 amp diode at 110 or 220 vac, 2000uf x 2 or x4 caps at high rails and auxiliary for the ir2153 u need to use external transformer to supply enough current and stable at high power or when u push smps to peak.