Hi Lucas,
We are sorry for the inconvenience.
We are unable to reproduce the reported issue at our end. We are able to load the toolbox with icons for Syncfusion controls in Visual Studio 2015.
This issue may occur, when using the large DPI settings. We would suggest to change the DPI settings to smaller option, if it is set to largest one(For Windows 8 and Windows 10).
Once you have changed the DPI setting, please restart the Visual Studio with administrator privileges and Reset the toolbox.
If this is also not worked, please follow the below steps to completely reset the toolbox,
1. Open the below location and view all the hidden files. Then delete all the .tbd files from the following path.
TBD files path : %localappdata%\Microsoft\VisualStudio\14.0\
2. Reconfigure the tool box by following the steps suggested in the below documentation link,
Doing so will configure our Syncfusion controls in toolbox and we hope that icons will be loaded this time.
Regards,
Manivannan S.