Hello,
I have a reasonable amount of experience with battery discharging gained from the nuclear power program in the RN & also have a small off grid solar power system.
A few points:
1. As other posters have stated, battery selection is important & a battery capable of being deep discharged necessary. I use Rolls batteries they seem very good.
2. Your stated load of 10 * 15W is 150 Watts at a nominal 12V DC equates to a load of around 12.5 Amps. You need to look at the discharge curves for your battery to see how long the run time will be at this load (it is not linear). Your battery should NEVER be discharged below 10.5 volts below that voltage it becomes scrap metal - unfortunately below 10.5V it would not accept a full recharge & performance severely degraded.
3. Be aware that batteries are generally specified at the 20 hour rate, this means that the battery is discharge over a 20 hour period at a set discharge to 10.5 volts so for an 80 Amp/hr battery this would be approximately 4 Amps. Your load is around three times this so it would mean the battery would be fully discharged in around 6 hours or so. This of course assumes a fully charged battery 100% capacity.
4. If you deep discharge a battery 100% to 10.5 volts you will find it will provide a lot less cycles than if it were discharged to say 50% or less - Your manufacturer should be able to provide this info.
5. The next issue is will your solar panel re-charge the battery the next day?
I would say you probably need a couple of hundred watts of panel, I have 4 * 100w & they sometimes give around 28-30 Amps on a sunny day (in SW France) if that helps. Dull days a lot less.
If it were me wanting to run the lamps for a full six hours, I would probably select a 200 A/hr battery because it would not be fully discharged & last (in years of use) a lot longer than your 80 A/hr - all depends on how long you wish to run for really, if say, 2-3 hrs then 80A/hr would probably be fine at that load.
Hope this helps
N