Greetings,
Newbie w first post and possibly silly question. I will be growing outdoors but am starting plants from beans indoor this winter. I will be vegging at 18/6 and plan to move outdoors mid-May/June depending on our spring. Our longest day here is 15.5 hours so I’m considering going to a 15/9 vegging schedule before hardening off the girls. Good idea? Bad? Not necessary? Thanks for all the great info here, been trolling for a while.
Peace
As I understand the mechanics of flowering, no - 15/9 will not induce flowering.
Doing so may slightly lessen your veg growth (less hours of light), but otherwise won’t be harmful or necessary.
My thoughts are that they will only be getting 15ish hours outside and maybe a 15/9 schedule for a week or two would acclimate them and reduce stress. Maybe I’m overthinking it.
Welcome to the forum. I have heard people stepping down from 18/6 to something like 15/9 on the way to 12/12, but, otherwise, like @blackshirt said, it’s probably not enough to trigger flower.
Indoors your plants need 12-12 to flower. I veg on a 16/8 cycle and they do just fine 
Excellent info, Thanks everyone! I started reading about the risks of re-vegging and was concerned that I’d induce flowering before moving them outside. No worries now. This entire project will be an interesting experiment anyway. I plan to journal it all and I’m sure I’ll be back w questions. Thanks to all and may 2019 be the best year ever.
Peace
I also veg under a 16-8 schedule and found that anything less then 16 will not allow them to flower but they will start to show signs of maturity and sex as soon as they are old enough
12-12 will still need to be initiated to get actual flowers @Verndoc
I have flowering plants outside now 530 sunrise 9 dark. I started flowering indoors. They are certainly not reveging but not growing great either. They are growing though.