Is the DB under heavy under heavy load? Like too many writes? If so you could try 'read replicas'.
These two articles are great for optimizing MySQL:
Can you move the entire DB to Postgres? Moving it won't be that hard. Postgres have much better performance than MySQL. The syntax is almost the same, so you won't need to change a lot. If so you could also take the advantage of Citus for Postgres
Beyond a point, DB can't be optimized. DB is always a bottleneck! Is it possible to cache the results in Redis?