Late response, and you probably solved your issues by now, but what is "lots of vertices"? Thousands, millions?
If you get over 100k vertices per polygon or line geometry, things can slow down dramatically. E.g. in a custom Python scripting and generalizing workflow, I've been processing data with records of up to 1.7M vertices per polygon in a PostGIS database generalizing them. I discovered by monitoring pgAdmin, the database management software of PostgreSQL, that it could take half a day for a single record to be processed when dealing with geometries > 1-2M vertices.
I don't know if it is acceptable for your workflow, but by dicing them to 100k vertex limit, processing times were dramatically improved. E.g. for one medium long running dataset (although not containing that 1.7M monster polygon), it reduced processing times from 1h23m to just over 4-5 minutes.
Dicing may not always be acceptable, but in my case it was, and it helped solving the performance issue.
