Normally it's recommended to only draw down these batteries to about 50% if you want any sort of extended life from them , but you could safely draw 1.5amps from that battery for 8 hrs without doing any damage.
Basically you are drawing 12v x 1.5a = 18wh , a 40W panel would come close to covering this usage while adding back some charge to the battery in good conditions.
A basic 12V 5amp regulator would be fine .
A lot depends on whether this supply is needed 24/7 or how many hours per day or night it's needed , if not critical the panel size could be smaller and the battery drained even further down to about 80% max occasionally as long as it is recharged quickly.
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