On my machine (MacOS, 2.7 Ghz i7, 16 GB RAM, 750 GB SSD), IntelliJ IDEA performance is quite acceptable. Some students, particularly those running Windows on older machines, have complained of slow compile and test times.
As a first step, if IntelliJ does not load within 10 seconds, the most likely culprit is your virus protection software. Please make sure your virus protection software is not checking the binaries or jars of IntelliJ on startup. The most simple test is to entirely disable virus protection and see if that fixes performance problems. If so, then selectively re-enable protection to avoid IntelliJ impact.
If it’s not your virus scanner, then the second most likely culprit is that your laptop does not satisfy the minimal requirements for this course. Please take another look at Laptop Requirements. The lack of enough memory or the lack of a solid state disk can be problematic. Note that an underpowered laptop will become even more problematic as the course continues.
Here are some posts that have worked in the past for IntelliJ users. But this is for older versions of IntelliJ, so it is quite possible they might not have any effect at present.