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, and you are using Windows, the most likely culprit is your real-time 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 real-time 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.
The third most likely culprit is that you are loading a lot of plugins. You do not need the vast majority of the plugins available for IntelliJ, and the more plugins you have activated, the longer it will take IntelliJ to start up. To diagnose this, go to Preferences / Plugins / Installed and check what plugins are installed in your system. The only plugins you need for this class are those for HTML, CSS, Javascript, and Meteor. Try disabling all the other plugins. The system should prompt you to restart. See if that helps.