Is 150mW a lot to dissipate from a TO-92 in 50°C free air without heat sink?
According to the datasheet it can dissipate up to 0.5W at 50˚C ambient temperature, which would make the maximum temperature about 150˚C. This leaves plenty of room for derating in long-term use, so you shouldn't have problems. Additionally, you could keep the leads short and use the PCB for a bit of power dissipation.