The better is draw the current less than 1/3(200mA) because the heat, if you want to draw more than you better prepare a heatsink, if you want to drive the MOSFET then 555 no needs the big current.An NE555 supplying 200mA at ~15V seems much better. But I need a good circuit. And I will also need to adjust the frequency.
Why you want to use 555, is that because it is cheaper?
Why you need a variable frequency, how about a crystal oscillator(4 or 10 Mhz) and some counters as frequency divider (CD4518, CD4013, CD4040)?
NE555 Pulse Generator and PWM adjustable circuit.