I have 2 LEC315 in my 5x5 and I can say it is not quite enough light. My temps stay like 63f with lights on so I can say its gonna be easy for me to throw like a 600w HPS in there for the next run; which is what i'd suggest.
2x LEC315 with a 600w HPS imo would be prime as hell in a 5x5. Chopping this tent in like 2-3 weeks then i'll be throwing another light in.
That being said i have 4 huge plants taking up literally the entire 5x5, if your plants are a bit smaller and dont entirely fill your entire 5x5 you might be able to get away with it
I love the lights I honestly do, I just think you need a little more juice for a 5x5