Hi Ivugrinec, jumping over more than 2 main releases is not supported. Also, 15 and 18.4 codes have major changes, instead try to move first to: 15.1X53-D58 or 15.1X53-D590, and then move to 18.2 before getting to 18.4.
""You can skip no more than two releases when upgrading (or downgrading). That means you can upgrade only to one of the three releases subsequent to your current release. If you want to upgrade across more releases than this, you need to perform multiple upgrades.""
The 2 release jump limitation, is more or less precautionary. The jump should actually work, but are you sure you have the right EX2300 image? I think you would be best to land on (at least right now) 18.2R3-S1. The image name should have "arm" in it. The image I found for EX2300 (includes -C and EX3400 as well) looks like this: