Q: iPhoto or Photos? HELP!

1 - maybe - getting rid of either will not save much space so the best plan is to keep both for a few months until you are sure that you are happy with Photos ( you might need or want the iPhoto library  in the future)

2 - obviously iPhoto contains all photos since that is what you have as a starting point - so then check Photos to see that tit has the same number of photos in it

3 - while the libraries look large they share hard links to the original photos and the previous do not use much more space in total than either one does - Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

LN