Question: Our little boy is 2 years old, and we are still giving him a large amount of formula milk at bed time.

He is not a good eater, and we don't want him to get hungry in the night.

Is it recommended to give extra milk (he often has at least 15 fl oz), or to let him go hungry so he is forced to eat his food?

Answer: 
If he is old enough to verbally communicate that he wants bobo at bedtime, then he's old enough to understand you telling him to eat his dinner.

You're not going to initiate direct change of this habit without a significant amount of stress. what you can do tho is change it indirectly.

Since the goal is better timing for getting full, you might load up at dinner on foods he likes (meal foods, not fun, snacky (read: processed) foods) and completely change brands of formula. you would then, *indirectly* entice him to change his habit. it would probably result in shifting his sleep habits and diaper changes as well. 

However...

My opinion is that I don't think you should force the issue. I'm generally not a fan of attempts to line-up a baby, in some way, with parental sensibilities. Kids this age are driven as much by what their body is telling them as they are by habit. They age (mentally) quick at this age (a baby's brain is more active at ~2-2.5 yrs than at any other time in life) and my opinion is that you should be patient. I'll bet that if you gave it some time (unless this has already been going on for weeks or a couple months) that the routine will change soon enough anyway... when their body is ready... like the next growth spurt.
Once he drinks your pediatricians quote of whole milk and maybe a bit more he has to learn that meals are meals and really food is what big boys eat. Ensure that he does his best at dinner, reminding him that breakfast is far way. Then slowly wean him off of snack (if bed time is many hours after dinner obviously don't take snack away entirely) and convert that snack to include solid food. He is a person and needs to eat like one, not like a baby any longer. This is not making him grow up too fast, it is teaching him proper eating habits while you still have the power to interviner in his activities.