Ubuntu 15.04 Vivid Vervet is great. I found this more stable and slightly more fast than previous version, especially in Ubuntu MATE edition. But sadly, there is one trouble and I guess this one is a bug issue in Ubuntu 15.04 Vivid Vervet. The problem is the Wifi (WLAN) connection in Ubuntu 15.04 Vivid Vervet is very poor and always got weak signal even if my laptop is near the wifi router. The connection also always disconnected periodically. I've tried Ubuntu desktop, Lubuntu, Xubuntu dan Ubuntu MATE and the result is same.
Later, I've also tried Ubuntu MATE 15.10 alpha, and the bug still presents. Hope in the upcoming final releases, the Ubuntu team could fix this bug.