Whether you will be laid off or not, the best thing you can do is find another job and move on.
This will leave a good record on your employment history.
Before your new employer hires you, they do a background check.
If your current status is "Employed", they are more willing to hire you.
If you are "Unemployed", they may think twice and question your capability.
Why are you the bottom 15%?
When you leave the company, you will do an exit interview with HR.
If you leave by yourself, your record will be "Leave voluntarily"
It is better than "laid off". Your future employer will like the former better.
So Why Wait?
Instead of asking "Am I safe?", "Will I have job in 2 or 6 months?", find another job and move on.
Don't worry what your decision will affect the project.
Someone will figure it out. Nobody is irreplaceable.
Good Luck.