1)…you used 7.5wt oil not 15wt oil because you already had some 7.5

2)…you didn’t use new crush washers because you didn’t read the instructions thoroughly

1) No
2) No

Magic, thanks.

How about 7.5wt instead of the 5wt damper oil? Will they just compress / rebound a touch slower?

Yep, it’ll just slow the damping a bit. You might like it, you might not, you might not notice anything! 🙂

Depends whether it’s Rockshox oil or some other brand – the viscosity varies widely regardless of the wt on the bottle, might even be exactly the same as your Rockshox 5wt.