PSE 15 won't recognize .cr3 files

Unfortunately, as far as i know, Photoshop Elements 15 can only use up to Camera Raw 10.5 for the plugin.

You can, however, while your deciding about PSE 2025 use the Adobe DNG Converter to convert the Canon 90D cr3 files to dng copies which should then open in PSE 15.

https://helpx.adobe.com/camera-raw/using/adobe-dng-converter.html

your camera requires ACR 11.4.

The max version of ACR for PSE is ACR 9.6-   and that is your problem.   

You can google Adobe camera raw version 12, and if you find a download tyou can manually install it to where it needs to go to---  that involves file renaming/ deleting and copy and pasting 1 file into the correct location-  many users screw that up the first or second time.

Your current software is about 8 1/2 years old- and for software that's getting "Long in the tooth".

OR

give the 7 day trial of PSE 2025 and your problem will be solved. 

https://www.adobe.com/products/photoshop-elements/free-trial.html

Yes, upgrading to PSE 2025 should help,

because it uses the up-to-date version of ACR plug-in.