Hi,
The top level page nRF5 SDK Documentation Library page (https://www.nordicsemi.com/DocLib/Content/SDK_Doc/nRF5_SDK/v15-2-0/index) contains a link to "S140 SoftDevice v6.1.0 (API documentation)" (https://www.nordicsemi.com/DocLib/Content/SDK_Doc/nRF5_SDK/v15-2-0/PLUGINS_ROOT/com-nordic-infocenter-s140-api-v6-1-0/index). When you click the link, it returns PageNotFound (error 404).
Thanks