How can I change the speed of slider using arrow in Slick Carousel?

I have created a logo slider which displays similar to marquee. What I want to do is to add next/prev arrows that can accelerate the speed of slider when click next arrow and reverse the slider when click prev arrow. I currently use slick carousel to make it.

Also I have no idea why sometimes my carousel pause for a second then continue, can anyone help me with this?

$(document).ready(function($) {
  $('.marquee-logo').slick({
    autoplay: true,
    infinite: true,
    autoplaySpeed: 0,
    slidesToScroll: 1,
    slidesToShow: 5,
    arrows: false,
    cssEase: 'linear',
    speed: 6500,
    initialSlide: 1,
    draggable: false,
  });
});

<div class="marquee-logo">
  <div class="slider-logo">
    <img src="http://placehold.it/350x150">
  </div>
  <div class="slider-logo">
    <img src="http://placehold.it/350x150">
  </div>
  <div class="slider-logo">
    <img src="http://placehold.it/350x150">
  </div>
  <div class="slider-logo">
    <img src="http://placehold.it/350x150">
  </div>
  <div class="slider-logo">
    <img src="http://placehold.it/350x150">
  </div>
</div>

http://codepen.io/takumi24/pen/JRzEjA

This can be used to make slider slow

 $("#slowbutton").click(function(){

 $('.marquee-logo').slick('unslick');

 $('.marquee-logo').slick({
  autoplay: true,
  infinite: true,
  autoplaySpeed: 0,
  slidesToScroll: 1,
  slidesToShow: 5,
  arrows: false,
  cssEase: 'linear',
  speed: 10000,
  initialSlide: 1,
  draggable: false,
  });});

This for making faster

  $("#nextbutton").click(function(){
  $('.marquee-logo').slick('unslick');

 $('.marquee-logo').slick({
  autoplay: true,
  infinite: true,
  autoplaySpeed: 0,
  slidesToScroll: 1,
  slidesToShow: 5,
  arrows: false,
  cssEase: 'linear',
  speed: 300,
  initialSlide: 1,
  draggable: false,
  });
});

http://codepen.io/anon/pen/yawgra

On button click first destroy the slider and add slider again with increased/decreased speed

You can also try by this $('.marquee-logo').slick('slickSetOption', 'speed', 500,true); with out destroying the slider

But speed change by slickSetOption method cause a delay:issue https://github.com/kenwheeler/slick/issues/2334