Same here! My baby is also 1.5 mo and does the same. I think it's fine when the other day feeds are regular and of similar quantity throughout the day. I let my baby sleep as long as she wants at night and trust that she will wake up for feeds when she is hungry. My baby slept through the night for about a week but just last night she wanted a 3am feed. I keep track of wet/ soiled nappies to make sure she's hydrated :) She's also gaining weight so I'm not worried.
For me, I usually don’t wake my kiddo up for milk, eventually they will auto wake up crying for milk after sleeping through out of the night. Baby know when they are hungry.
If diaper output and weight gain is ok then that's alright. Sleep is important for babies' development too. But if you're worried, you can always dream feed her
Ur so lucky, how I wish mine can sleep so long