I can't quite believe either of the values you mentioned.
1 Mio processes in 8 secs? That would amount to 0.008 ms per ProcessInstance. With DB Access?
On the other hand your 7 sec. values sounds like something else is wrong.
jBPM itself definately isn't slow. The last app I built had a throughput of 1 Mio. Processes / day. No problems. (Ok. Bigs AppServers, but no fundamental problem... :-)
Greetings from Bern