Knitting pattern and smaller needles

Hi there, new here and in desperate need of help! I am pretty new to knitting and taking on my most complex pattern so far. The problem is - I can’t see it! In the parts with pattern, it isn’t turning out very defined even though I’m knitting tightly. I AM using much smaller needles than recommended - the yarn said US size 15, which was WAY too big, but my next smallest was a 9 and it was working fine. My question - is using that much smaller what’s affecting my pattern definition? Or is it maybe the yarn or something else I’m doing? I tried the whole block of that pattern hoping it would become more visible, but it really didn’t. It’s for a gift for my mom so really wanting to get going on this and no idea what I’m doing wrong!

would you be able to post pictures of what you are making vs what shows up in the pattern picture?

Welcome to KH. What are you making and can you post a link to the pattern or a picture of it? If not, what is it called?

Different yarns work up differently. It could be a yarn and needle size problem or it could be that your yarn just isn’t going to have the stitch definition needed. So we also need to know more about your yarn.