At the moment on trunk org.apache.tomcat.util.threads.ThreadPoolExecutor#contextStopping does a sleep(200). Would be great to be able to remove it. This is an issue in particular when using arquillian and if you deploy several small wars - one by test. On BVal TCKs in TomEE it makes tests during ~6mn on my machines so removing it I can gain (758 test * 200 ms) = 151s (looks like a big part ;))
I don't see any reason for the sleep. I have removed it. The fix has been applied to 8.0.x for 8.0.11 onwards and to 7.0.x for 7.0.56 onwards.