Pattern help

Hello!
I am currently working on this pattern. https://www.yarnspirations.com/caron-diagonal-stitch-knit-cowl/CAK0110-009962M.html

I have 2 questions
1. I know the pattern calls for size 11 needles but would size 15 needles work (only large needles I have)?

 2. I am having trouble figuring out a row. "K2tog, but do not slip stitch from needle. Insert right hand needle between sts just knit tog, and knit the first st again, then slip both sts from needle."
   Does anyone know what this may be called 
   so I can look for a video tutorial on it? 

Thank you in advance!

If you use the yarn recommended in the pattern, the larger size needle will give you a more open, lacier stitch pattern. Of course, this also depends on how tightly or loosely you knit. Best to knit a swatch with your yarn and needles and see if you like the resulting knit fabric.

The stitch you’re describing is a right twist.

Awesome! Thank you so much for all your help!!