Xr15 or xr 30

[trippinoutreef]

I currently have two XR30 over my LowBoy tank. I have an additional lowboy mounted right by it. I am wondering if I should do two more or just add two XR15?

 

[X-37B]

I currently have two XR30 over my LowBoy tank. I have an additional lowboy mounted right by it. I am wondering if I should do two more or just add two XR15?

If you are having good results go with 2 more 30's. 2 15's dont make sense to me unless you want less light?