@skenow indicated correctly that in fact, what we have been doing in the context of 1.5.0 has realised almost everything of what was initially (10 year ago) identified as what was the target scope in the 2.0 release. As a result of that, we will do a version reshuffle and instead of releasing 1.5, that version number will become 2.0.
@mekdrop has done a great job in fixing the last lingering issues in that codebase that were preventing it from running on current PHP versions (8.0 and 8.1, not talking about 8.2 just yet), so a new RC is right around the corner. Only that new release candidate will be the 2.0 RC, and not the 1.5.0 one...
We have tested the code starting with PHP 7.4, so no guarantees below that version. Your mileage may vary depending on what you use on your specific site. Also, if your modules have not received recent updates, chances are that they will not be 100% compatible with the newer PHP versions, which is more likely than not being compatible with the new ImpressCMS code.