15k isnt bad to work with, the no posting for a month is your bigger problem honestly. Algo basically stopped pushing your stuff so you gotta warm it back up before anything else. Post consistently for like 2 weeks first, get engagement moving again.
For actual money without monetization... depends what niche the page is in tbh. If its something with buyer intent you can do affiliate links in posts, or just sell shoutouts/promo posts to other pages in similar niches. People pay decent for that if your reach is real. Also you can flip the page itself, 15k sells for something on the right marketplaces but not much if engagement is dead.
@tigri09 whats the niche and where are the followers from? that changes the answer a lot. A 15k US/UK audience in a money niche is worth way more than 15k from tier3 countries.