OK, those times are a bit slower than on our Jobe server, but not hugely. With those numbers, and if you're using a question type that doesn't make use of a combinator template, I'd expect a 6-test-case question to take around 7 - 8 seconds. This is long enough to be a bit tedious but isn't too bad, I think. However, you said you had a 12 second delay so ... are the tests themselves taking significant compute time too?
Perhaps you could tell us more about the question you're using: the question itself, the template(s) and the test cases? Is it fundamentally necessary to compile a different program for each test case or are you just running the same program over and over with different input?
Without knowing the specifics, the only suggestions I can make are:
- Reduce the number of test cases by packaging multiple tests into one.
- Use a question type that uses a combinator template, such as the supplied java_method type. Combinator templates package all the test cases into a single compile-and-run, so you'd then get a response time of just a couple of seconds. Note that if you edit the template of such a question and wish to get the speed-up from the combinator, you'll have to re-enable it (assuming you clicked OK when the dialog popped up warning you) and add your custom code to the combinator template as well as to the per-test template.
- As a variant on the above, you might be able to use a Python question (with a combinator template) as a script that compiles the Java program then runs it one test at a time. However, this requires advanced CodeRunner skills and is not recommended for newcomers. It's also important to know that the combinator template won't be used if the test cases have any standard input, so any such input would have to be placed in one of the other test case fields (e.g. the Extra Template Data field).
- Get a faster server :)