Hi Benjamin Foord,
Thanks for using Syncfusion products.
No, LightSwitch Extensibility Toolkit is not needed. We can use our Lightswitch HTML Extension in VS 2015.
For your reference, we have prepared a LightSwitch HTML Date picker sample in VS2015. You can download the sample from below location.
Sample Location:
http://www.syncfusion.com/downloads/support/forum/119803/ze/Application11634911819
Please let us know if you have further queries.
Regards,
Gobalakrishnan S