@Anonymous
Simply by opening them up in Inventor 2017 and saving them. If you have numerous ones you can use the Inventor Task Scheduler to do this.
Also if you have a drawing that has styles written back to your design data folder in 2015, then you need to run the Inventor Style Library Manager to convert those drawing styles to the 2017 version.
Mark Lancaster
& Autodesk Services MarketPlace Provider
Autodesk Inventor Certified Professional & not an Autodesk Employee
Likes is much appreciated if the information I have shared is helpful to you and/or others
Did this resolve your issue? Please accept it "As a Solution" so others may benefit from it.