I have an Odroid XU4 running Debian Jessie and NC 12 and have successfully compiled OnlyOffice on that platform (that is, almost successfully, there are some issues which still need to be resolved, see here https://github.com/ONLYOFFICE/DocumentServer/issues/152, https://github.com/ONLYOFFICE/onlyoffice-owncloud/issues/96).
Compiling takes an awful long time, but I can confirm that performance-wise, OnlyOffice works well on this ARM-based platform. XU4 is faster than Raspberry, but cheaper than an Intel NUC.
Would be great if more people would try to compile/run OnlyOffice on ARM-based platforms, such that we can get to a fully working image eventually.