I'm guessing you just want off 1.5, correct? You can go down to 1.4, or anything higher than 1.5.
As a data point for you, I have one Phantom on 1.4 and one Phantom on 1.6. The only real difference I see is that 1.6 (and higher) has the "propulsion limited" warning added as the safety protocol to correct the issues with 1.5.
If you are just trying to get off 1.5, maybe try 1.4 again to see if it's stable for you. You can always go up from there, but if you go to 1.6 or higher first then 1.4 is no longer an option for you.
As
@UKFlyer noted, it's a personal choice up to you. Good luck!