2 days late, still no dark positive line

A

I am 15 dpo today, 2 days late on AF. I took a test this morning and there was definitely a light pink line, but I guess I thought it would be darker than just a light pink line by now? I see a lot of women getting very dark positives at 15 dpo and I am scared that if I do end up being pregnant that my hcg is rising really slow. Have any of you ladies had your dark positives come a little later after missing your period?