Cashing out employee stock purchase plan

Hey guys I might be leaving my job in the next month to take another one and I've recently thought about cashing out my stock from my employee stock purchase plan.

I have 15k in it as of now and contribute $100 per paycheck to it and they buy stock at the end of every quarter for a 15% discount.

My question is, what are we looking at with taxes on this and is this something they tax when withdrawal or at end of year?

Also what happens to that money I contribute every check if I leave in the middle of the quarter?



Thnks in advance