i think in 3 Monts

That means three more months for me to distro-hop.  If Deepin 2015 is nearly as great as I anticipate, I'll be stuck on it for a while.  

It wille be Deepin 2016...

It will be different. This release is based on Ubuntu. Ubuntu is based on Debian. The next deepin release will be based directly on Debian. Ubuntu can use just about everything written for Debian, but not vice versa. About one-fourth of the Ubuntu repository won't run on Debian. So the transition will probably have a few bumps. The development team will do everything possible to pave the way in advance, but if you are running some very obscure apps, you might want to do a little research now. Look before you leap.

the alpha1 is not very decent, lots of things are not functioning properly, to certain extent a1 is not even as good as 2014.3.

Where I can download deepin 2015 beta?

I'm not sure exactly how this works, but alpha1 is out and should be smoothly upgraded to alpha2 in the fashion of a rolling release. There is a closed beta testing team that provides feedback to the developers. This phase ended in July. Tomorrow there is a conference in Beijing, which will almost certainly feature updates. Right now I don't know of any download source for deepin 2015 beta. I'm not even sure they will call the next phase beta.