I dunno if it's a typo or not, but I think it's 1.5m since I recall beating V1 post Reflowering and I've been fighting the V2 a lot and didn't have trouble taking her out after she did it. Then again, it may be cause I've been doing so much damage to actually notice it.
EDIT: Yeah, definitely think it's a typo. I've just tested it on V2, who also has 15m HP, after she did Gensokyo's Reflowering. I did between 6m+ damage to her before she got to her next turn. Her next move was Focus, which she'd normally do with less than 5m HP, and fell to 3.7m+ damage afterwards. So I don't think the skill fully restores her.