Approximately what core temperature is required for a protostar to ignite sustained nuclear fusion and enter the Main Sequence?

Answer

Around 15 million Kelvin

Sustained nuclear fusion, converting hydrogen into helium, ignites when the protostar's core becomes hot and dense enough, which is specified as approximately 15 million Kelvin.

Approximately what core temperature is required for a protostar to ignite sustained nuclear fusion and enter the Main Sequence?
evolutionstarmassstage