You’ve written Posts IDs – 15541,15129,15127,19 in Posts Slider element settings, but there are no such ids for your posts. Remove them from there.
Concerning the images please add this code in custom.css file:
.product-content-image img {
height: 400px;
}
How to create custom.css you can watch in this tutorial (it’s for Legenda theme but the process is the same).
