SEO advice - combine small sites into one large?

I have a network of niche sites that, over the years, are in a category that has expanded.

Now, those 15 sites should really be 50+ sites if I continue keeping them niched down, but there is a large crossover of users and content between them.

From a work perspective, after the initial work of combining the sites, sifting through content to avoid duplicates, and 301 redirecting everything, the ongoing work would be greatly decreased as I would have one large authority site to manage, deal with, and create content on.

From an SEO perspective, I will create a new 'brandable' domain for the authority site. With 301 redirects, should I expect this to cause a setback, or would this new domain be very quickly recognized as an authority since I would have my existing and aged 15 sites pointing to it?

Thanks!