Present concurrency is 0, it's just slow. It's not SQLite unless there is pathological behavior because I've demoed ideas to HN traffic with SQLite before and it performed better than a vanilla MySQL deployment. (Not saying this is advisable, just that SQLite isn't at fault unless Trac is doing something stupid.)

Are you positive switching to the postgres backend will help when there's almost no concurrency and the slowness is persistent and deterministic?