Board Thread:Game Discussion/@comment-33787703-20180717072943/@comment-34314527-20180719030630

Eyespy wrote: The career changes post says they are moving the 2015 cars out of career so they won't be in EL. >You will keep your cars and upgrades and can use them in Endurance Prototypes and Endurance Legends.

That's a direct quote from the blog from the section on the 2015 prototypes.