You have less than a month to upload all the images you want on Google Photos without having to pay anything for additional storage. As Google announced late last year, any "high quality" photo or video you upload to the service will count towards a 15GB limit after June 1st. That cap will be shared with your Gmail, as well as your Workspace documents, slides and spreadsheets, so you'll have to be smart when it comes to backing up your snapshots. Any high quality file you upload before June 1st won't count towards the limit yet, though, giving you some time to fire up the app and make sure your pictures are uploaded to the cloud.
Currently, the Photos service provides unlimited backup for high quality media files, which are slightly reduced in quality from the original. Storage is only limited for files uploaded in their original format. After June 1st, however, you'll have to pay for a Google One storage plan if your photo uploads and Workspace files go beyond 15GB. The cloud service will set you back $2 a month for 100GB of space, and there's also a 200GB and a 2TB tier that will cost you $3 and $10 a month, respectively.
If you have a Pixel 2 or a newer Pixel phone, though, you don't have to worry about hitting a limit at all. You can keep on enjoying unlimited storage for free, so long as you upload from your Pixel.