Hey guys,
Had the same problem a while ago.
Instead of waiting or downloading a beta version I emailed sketchup and told them my situation.
They were able to send me a temporary pro license activation code for SU2014 so that I could use my Maxwell
Render plugin for another while.
Taking in to consideration that plugin for SU2015 is not fully complete I might ask them for this favour again.
It is definitely worth a try.
Good luck!