
How is a 10g too small for anything? Not sure how the problems with your 15g are indicative of everyone else either.
I have a 20L reef tank (about to set up a 10 also

) and it has absolutely no nuisance algae. It only looks better and becomes more stable the longer it's set up. In fact I'm about to put my 3 large snails in our 90g because I'm having to supplement with dried seaweed so they don't starve. I have a coralbanded shrimp, some kind of goby, several corals, my colony of star polyps is getting HUGE and everything is spreading. I use distilled water for the changes and to top off and I think that significantly helps keep algae away. I have 124 watts of light on it right now, so if algae was going to grow it would but instead I have lovely purple rocks from so much coraline.
As far as the lights heating the tank too much all I did was raise the lights a bit and point a fan at the tank. Problem solved.
I don't have halides, which would significantly mess with the temps, but you don't need halides on such a small tank for beginner or low light corals. It's also debateable to need halides for some corals labled as needing such since I know several people who keep lovely LPS and SPS with nothing more than power compacts.
There are pros and cons to smaller tanks.
Pros - Less water to change out. Easy just to buy bottles of distilled and mix salt than producing your own water or having to use tap. Easier to work with because you don't have as much to maintain. MUCH cheaper to set up, requires a lot less light, rock, sand, etc.
Cons - Needs to be watched closer (if something dies in a 200g tank it probably won't change much). Less options for stocking.
Honestly if you stock a very large tank heavily it's NOT going to be any easier than if you stock a small tank properly. My 90g doesn't need to be watched very close because it's extremely lightly stocked, but it's not near as fun to look at, IMO, as my little 20 long with all the corals and other creatures.
BTW, I've seen some fish stores with some BEAUTIFUL 10g nano reef tanks and even smaller.