OK, this is a Metal Halide (MH) system.
The light from these is typically very blue and white. Flowering plants will favor some red. The newest MH systems have begun to try to get more red output.
The T5 is a good set up. I love mine for veg. I have flowering bulbs (red fluoro) I may use this time around for expedience. These are very affordable and I bet they work too. Never tried.
I would definitely stay under the fluoro until you are ready to go to 12/12. Daily, lower the fluoro light a little, and eventually, bring it within 16" of the canopy and watch the little devils dance.
The 315 MH is actually an optimal veg light as well. Should flower ok. Start this fixture roughly 40" from the plants and very gradually move it to within about 24" of the canopy. Raise, if possible, as needed, it should get hot and will be more prone to burning your plants.
One last item, the variable settings on the MH 315 are nice, but this unit will run inefficiently (same juice, less light) on all setting but the highest, pretty sure.