How to reduce photo resolution within iPhoto
I have a lot of pictures in iPhoto taken at 12 MP that I know I'll never need to do anything with at very high resolution. I want to be able to still see them full screen in iPhoto, but I don't need them be quite so high and have a file size of 3-4 MB each. Is there a way within iPhoto to selectively reduce the resolution of photos? I know I can export them, reduce them with other software, then import them back, but this is not a feasible option for thousands of photos. Thanks for any help.
iMac, OS X Yosemite (10.10)