What will be the impact of optimizing the images on my website? How much load time will be reduced?

There is no easy way to answer this. Page speed depends on a lot of factors, like heavy images, tracking scripts, HubSpot templates, server-side programming etc. With LitePics, the image compression is one of the factors that is taken care of and the speed will improve with respect to that only. 

If your page speed does not improve significantly, then we would suggest you get a free audit done, wherein we can tell you what other factors are hampering the page speed and what we can do to fix it.