When tests become too slow I make the code and or tests faster until the tests complete in under a minute. Running tests in parallel can help. Even so, with a large set of tests that might be easier said than done but perhaps you can trim them down to the set that are most likely to be relevant and start off by testing just those? There are fancy ways of minimising exploration, working out which tests are most relevant for a given code change, but that is probably for later. Better to get started and then expand!