Speed training will improve your speed to the ball and maybe get you that extra couple of tenths to setup correctly so you're not just getting to the ball but getting to the position before the ball arrives. I wouldn't necessarily agree with extra on top of 3 hours a day. I would like to see it incorporated in that 3 hour practice, but every coach is different and every teams needs are different. Either way it can be worth it if you don't slack it off.

I'd like to add a suggestion to never be known as, "That Girl." That Girl is the person who complains, talks behind other's backs, makes short cuts on laps, doesn't do every set/rep in training and consequently loses respect of coaches and players. That Girl gives no more than 75 % most of the time. Unfortunately, because every team is only as strong as the weakest link, the team suffers. (Please keep in mind I'm not trying to accuse you of being That Girl.)

However, I would encourage you to be "THE Girl." THE Girl may not be the most talented, but THE Girl is the first to practice. She is the loudest cheerer. She is the first to run to a teammate on the ground to offer a hand. She is the first girl to pull everyone in and remind them of their focus and encourage them when they're behind. THE Girl is the last girl to leave practice because she: a) stayed to work on her dives, b) stayed to help a teammate on her dives, or c) stayed to help take down nets. THE Girls is one that everyone looks up to because they know that while she can only give 100%, she strives for 100% and encourages her teammates to do the same.

When coach asks you to do something that seems a bit unreasonable, (and may be...) be THE Girl.

yes speed is important in volleyball cause u do not want to walk to the ball you want to run not run sprint and speed will help you play better and a better chance of winning

If you can get to that ball, you CAN run fast. You just need to do it. You have the ability to move your muscles quickly enough. It seems that you unlock your potential when you're doing something you enjoy. Try to make speed training into something that you might enjoy rather than that thing that's nagging at you all the time. So yes, it is extremely necessary for you to be fast. And as you say, you are fast. You just don't enjoy the training so you haven't unlocked your potential while speed training. Keep trying and never give up! Sorry I always answer these about a year late.
Also, if you want to know your coaches point of view on it, just ask him/her in a nice, respectful way. Try not to sound like you're complaining or they'll just wave off your question.