Yes, the problems typically get harder as you go along. Sometimes the questions get misplaced and 15 could be harder than 22 but in general they get harder. The tests are often discussed at length on the AoPS forums and AoPS has databases of the old tests with detailed solutions...oftentimes several solutions.
Check out the AMC 10's and 12's or the AIME...those get pretty tough.
One more thing, recent tests tend to be quite a bit harder than tests from 6-7 years ago...this holds true for all of the MAA exams, I think.
