Have a single light Sussex around the 15 week mark (hatched in mid October). Wanting some confirmation around gender (I know I probably won’t get a 100% until they lay or crow).
I'm not super familiar with the light Sussex, but plenty with the SS breed and for 15 weeks, our girls combs and wattles were HUGE, I don't see Cockerel so I'm going to guess Pullet, has the stance of a Pullet IMHO, but it's a guess for me.
Don't be fooled by the pattern making the feathers look pointed.. but starting around 12 weeks is when gender specific saddle feathers can be seen usually more flowing like the second example by around 16-18 weeks (on non hen feathered breeds). examples from google..
Your first photo looks like well rounded saddle feathers meaning I'm going with pullet, UNLESS the comb and wattles have been read for nearly 8 weeks already.
But with regards to not knowing until a bird crows or lays an egg.. uh NO, even hens can crow (quite pathetically) and grow spurs. It's true that a rooster will never lay an egg.. but neither will some hens as those egg follicles come form only one ovary and it may get damaged, not develop correctly, etc
From the time the ladies red up like that.. is usually about 4 weeks to the onset of laying in MY experience. Some will squat when you quickly put your hand over them.. a sign of submission and getting ready to be mounted. Some will never squat, depends on their personality.