There is no such thing as SATA I, etc. The system fully supports SATA 6G (which is misnamed III by many).  
this  is my laptop. I want to know what version of SATA does it supports?  It supports 2.5 inch SATA but I'm asking does it support SATA I, SATA II or SATA III? 
Dell Inspiron 15 5567, SATA I, SATA II or SATA III?