The LO15 have about 9-10mm Xmax compared to 15mm Xmax on the Dipole15’s. This allows the Dipole15 to play lower due to more volume displacement. How low and loud is really determined mostly by the baffle size and style. I typically target about 35hz as the minimum for the LO15. At 2 per side, you would have good output to that point.
If you wish to go below that, the Dipole15 or even Dipole18 is the better option. Typically only going up to 250-300hz, the Dipole will be the best option so you also get more low end extension.