Kitchen sink/dishwasher/garbage disposal drain size question

[JuanSigned]

I'm putting in a new kitchen sink drain and there is a space challenge that could be solved by using 1 1/2" ABS for the first part of the drain. The 2" line is already in place. My community recognizes the IPC 2012 code requirements. I don't see anything in the code that says this is forbidden, but I could have missed it.

So, what do y'all think?

 

[Terry]

We run 2" all the way to the trap arm.
Also, a 2" cleanout that is accessible. You may need to pull out the drill.
Does it work with 1.5"?
Yes, it was done that way in the 60's, not real well though.