Negative 15V supply from 24Vdc
You can use inverting charge pump, buck-boost voltage inverter or a virtual ground op amp based solution to split rails.  

This is one example component which can provide \$-15\,\mathrm{V}\$. It is a simple dc-to-dc converter module.

Part number: P7805-Q24-S15-S


Do not miss to notice the pin numbering in both configuration.