The rights needed by the K2 server account is with the assumption that your code is running from the K2 server. We give it admin rights because there will be instances that the process does admin functions such as creating a site.
Of cos from normal development from a standard user account, you would probably need rights to access the functions from the K2 Designer. e.g. enumerating the list of document libraries from a site.
Perhaps if you gave a bit more detail on how you are using the K2spslist function and your environment setup, it might help us in understanding your issue better.