I am missing photos from 2015-2019 from icloud. Can I recover them?

Hi!

It depends how long ago they went missing. If it was 30 days or less ago, open photos, Click albums, and scroll to the Recently Deleted folder. If you’re running iOS 16+, you’ll need to use your Face ID, Touch ID, or passcode to open it. If they’re there, you can recover them by selecting them, and hitting recover. If they’re not in there, check the Hidden folder. Same process as above.

If you have no luck there, then your luck may be out. Sorry!

For the future, I’d recommend sending valuable memories in photos to yourself on a laptop or desktop, and saving them in a local folder as a backup.

I hope you find them!

Only if they appear in your recently deleted album. Otherwise, you'll need to recover from your backups or original sources.