Upgrade Windows SQL standard edition to 15

If you are running SQL Server on EC2 then the recommended way is to launch a new SQL Server instance and migrate the databases to it. This can be as simple as detaching the data volumes from the old instance and re-attaching to the new instance. There are many considerations around High Availability, SQL Agent, Clustering etc which need to be taken into account when designing your upgrade path. This article from Microsoft does a good job of explaining the different methodologies i.e. in-place vs new instance vs rolling upgrade:

https://learn.microsoft.com/en-us/sql/database-engine/install-windows/choose-a-database-engine-upgrade-method?view=sql-server-ver15