Eclipse Mars will be landing in Fedora 22 repositories very soon! The update is currently in testing and you can help test it by installing it from the "updates-testing" repository:
$ sudo dnf --enablerepo=updates-testing update eclipse\*
Early adopters will probably know that Eclipse Mars is already available in the Fedora 23 Alpha that was released on Tuesday, which you can try if you are feeling brave; any bugs will be gratefully recieved. It is very probable that by the time Fedora 23 is released around Hallowe'en, it will be shipping with Eclipse Mars SR1.