I have the same problem. I installed a Debian 8.0 Jessie image from the internet
http://sjoerd.luon.net/posts/2015/02/deb...e-on-rpi2/. I had to install & configure WPA_supplicant package extra on that image, but WLAn adapter was recognized from the beginning. However, it seemed to be very slow, especially when using SAMBA it turned out to be too slow to make any SAMBA drive usable. This problem with internal WLAN speed i could solve by installing the "non-free contrib" package "realtek-firmware" from non-free debian jessie apt sources, but still my self-compiled Kodi 15 Isengard is not able to stream videos from the internet.
MP3 streaming seems to work at least partly. In the same WLAN network i tested Kodi on my Windows machines and it worked perfectly. Streaming videos was going smoothly there. I tried also to install on an Android device, but there was no add-ons available for installing thus, i was not able to test whether Android tablets could access internet streams via Kodi add-ons. However, i suspect that this would NOT work.
What i have observed is that on my router port forwarding is also done automatically in case of UPnP port forwarding. All my windows machines connected to the WLAN have some port forwrding entries concerning UPnP be it Skype, Tor or something else, but there is no entry for the RaspBerrry Pi 2 or for any of my Android devices. Maybe the problem is the way how UPnP is set up on the RaspBerry Pi 2? Maybe the role of the ADSL router is not respected or recognised as it should be, Kodi thinking that it is providing the UPnP services alone. In such case UPnP drivers maybe would need some configuration? Am i right? Solving that problem would maybe require to gain some knowlege in UPnP iinternals...
As for the video playback speed of RPi2. If Kodi is used to playback videos on USB attached hardware it is working nicely (BTW, i still have to check, whether Kodi can playback any multimedia files located on one of my Windows machines Samba (SMB) shares nicely..)