Don't just lower your budget because 80% of the companies do it right now. If you see great results, why not grow instead? Are you in e-commerce or SaaS? If so, determine ROI and use that + ROAS as KPI. If you are in a B2B or a service-related industry, go find out what the average order value and conversion rate from click to sales are to determine a maximum cost per acquisition (CPA). As long as you're reaching the desired ROI or CPA, you should be able to spend whatever you want (though that's not always how budgets work for companies, of course).