We just needed to set the resolution before loading the image.
$image = new Imagick();
$image->setresolution(300, 300);
$image->readimage($filename);
$image->resizeImage(1500,0,Imagick::FILTER_LANCZOS,1);
$image->setImageFormat('jpg');
$image->writeImage("1.jpg");
This code will convert a vector to a sharp and crisp raster image. It works for all vector formats (svg, ai, emf, wmf, etc). If the jpg result is unexpectedly a black image, you need to change the image transparency to white (check this link). Another way to get around with transparency problem is by getting your PHP updated to 5.5 and by installing Imagick for that version. By doing so, it will not cause any problems with transparent images and the above code will just work fine.
For testing purposes you could change jpg to png because it supports transparency.