JLPT level 1 *probably* won't be required for entry to your school.
If you were applying for admission by yourself, then it likely would, but for the government scholarship students, they tend to waive the requirement.
At my school, PhD candidates are technically not required to know ANY Japanese, as long as they can communicate with their advisors in English.
Since master's students have to take classes, which are mostly offered in Japanese, they are required to speak Japanese of course, but in my case, that was included in the interview portion of the entrance exam we were given.
If you already have a fair amount of experience with Japanese, you can probably pick up the more field-specific terms as you need them, so I think you could afford to skip the language training.