Does stamina recovery speed stack by wearing a Chloranthy Ring and a Grass Crest Shield?
Yes they do in fact stack.
Consider checking this: Minimum and maximum stamina regens DS3.
For further information on what does and does not stack in regards to stamina regen in dark souls 3 and for more info consult the wiki: Cloranthy ring DS3 on Fextralife. Grass crest shield DS3 on Fextralife.