Developer Ondřej Pokorný has made available version 1.0 of his OXml library which is a super fast XML parser compatible with Delphi XE6 & XE7 Firemonkey (and probably AppMethod). There are benchmarks on the OXml site which compare it’s performance against other XML libraries that work with Firemonkey and OXml comes out faster than the XML libraries that ship with Delphi (and speed counts on mobile). Reading over the architecture of the library it basically says that it uses pools of records to achieve the speed. The library is cross platform and compiles for Windows, Android, IOS, and OSX. Additionally, it runs in both VCL and Firemonkey. At the time of this writing there are only packages in the download for XE6 but I installed them and tested one of the demos in Delphi XE7 and everything worked well. You can set up OXml to be the native vendor on the TXMLDocument that ships with Delphi XE7 Firemonkey which should allow you to just drop it in and go. There is a small fee to use the library in a commercial environment.
Head over and download the full source code for OXml to test out in your Delphi XE7 Firemonkey apps.