Finding issues with STP45N65M used in a 500 kHz HB LLC Resonant Converter

Hi

We are using a  STP45N65M for a 500 W HB LLC operated at a frequency varying from 250 kHz to 500 kHz. We are using a driver SI8273 ( 4 A Isolated driver) with a Rg of 2 ohms. We are facing the following issues.

1. We were not able to get a rise time of less than 200 ns
2. The drain to source capacitance when measured shows 22 nf ( while the data sheet value of Coss itself is 82 pf. ) The problem with this is our Resonant capcitor itself is 5 nf. This capacitance makes the voltage across the switch almost sinusoidal when it is OFF. It's getting abnormally heated even with a very small input DC voltage applied..
3. Pls let us know is it advisable to use thos device for a 500 kHz application ? Pls suggest any compatible 1 MHz driver for this in case the one silabs is not advisable.

Thanks

Lenin.