Now I feel bad. I'm a 400/800 guy but I've raced longer pretty often:
800 - 2:04 1000 - 2:45 1500 - 4:26
I bet a lot of 400/800 types project to the 1000 and 1500 even worse.
OP is running more volume and doing 5k workouts. Most 400/800 guys would likely be right where you are.
Yeah, you're right on target for a 4/8 guy. For reference, I trained with a group of 4/8 guys for the later part of my running career, and several of them broke 2 for the 8 before breaking 4:30 for the 15.