Is the 2560x1600 screen worth it over a 1080p laptop?

Yes if you read a lot of text or edit photos. The higher resolution looks noticeably sharper, and the touch layer adds convenience. A 1080p matte screen still wins on battery life and glare outdoors.

Can I upgrade the RAM later?

Usually not. Most Dell 15-inch models with this chip solder the 8 GB of DDR5 to the board, so buy the memory you need up front. Check the specific model's service manual before assuming it is upgradable.

Only light ones. Iris Xe graphics handle older titles, indie games and esports at low settings, but modern 3D games will be unplayable. It is not a gaming laptop.

How does it compare with the Dell Inspiron 15?

This is essentially an Inspiron-class machine with a sharper touch panel. The Inspiron 15 typically offers the same processor with a 1080p screen, so the main difference is display quality versus battery life.

Is the touchscreen good for drawing?

It works for notes and basic sketching, but it does not support an active stylus with pressure sensitivity like a convertible 2-in-1. For serious drawing, look at a dedicated tablet or a convertible with pen support.