Papirus is an eyecandy suite for KDE desktop, jarkamirov ported Papirus icons for Ubuntu Unity desktop. These icons are recommended to only use with Unity desktop and currently no other desktop is supported but you can still try them, it may or may not work for you in other desktops. You can use Unity Tweak Tool, Gnome-tweak-tool or Ubuntu-Tweak to change icons.
Papirus KDE pack is specially designed to customize KDE desktop, it offers Plasma 5 themes, legacy support Plasma themes for KDE 4, icon theme with light dark panel icons, System color schemes, Konsole profile color-schemes, GTK themes only KDE 5 desktop, LibreOffice icons, Yakuake skins. This pack is available for Ubuntu 15.10 Wily/Ubuntu 15.04 Vivid/and Ubuntu 14.04 Trusty. You can change themes and icons for KDE by going to System Settings. I found a panel problem with Dark version of theme, hopefully new update will fix this issue, if you encounter any other bug then report it. If you are using other distribution with KDE desktop then download from Git repository.
Papirus Unity Icons
To install Papirus Unity Icons in Ubuntu 15.10 Wily/15.04 Vivid/14.04 Trusty/other related Ubuntu based distributions open Terminal and copy the following commands in the Terminal:
Papirus KDE Suite
To install Papirus KDE Pack in Ubuntu 15.10 Wily/15.04 Vivid/14.04 Trusty/other related Ubuntu based distributions open Terminal and copy the following commands in the Terminal:
GTK-Themes (Only for Kubuntu 15.04/15.10)
What do you say about Papirus theme pack?