iPhoto or Photos????

One question at a time helps

1 - which you use is totally personal - iPhoto support was discontinued well over a year ago and some day it will quit working - for people who only update every 5 years that is not an issue - if you install every update it is - and Photos have more features that iPhoto and a completely different work flow - so you fist need to make that decision

2 - once you make a decision on the software you want to use then you need to provide clear symptoms and questions about it including the version and the exact context

4 - as to space - no - when you migrate from iPhoto to Photos both libraries use hard links to the same original photos and the same previews so little additional space is used -- Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

5 - and you are three updates behind - your first move should be to update to OS X 10.11.6, the current version of the OS - that might or might not help things but is a good idea

LN

The first upgrade to new software often has problems and it may make sense to wait until the second release of new software (although most people do not and usually do not have problems) - after that the updates fix problems and are important

LN