Hcg 135 at 15 dpo — ok?

Hi, I went in for my blood test today and my hcg was 135. I’m 15 dpo now, and have had some spotting last night and this morning. My doctor isn’t worried, and I’m going to go back in later this week to see if it’s doubling, but I had a miscarriage this spring and am a bit panicked that the hcg seems low. Anyone have a similar number at 15 dpo? Did it turn out ok? Looking for any thoughts.