I'm not an expert with the SVG file format, however a quick inspection of the two files would indicate that the program used to create the original file (CorelDRAW X6) was horrendously inefficient. (Don't forget, SVG files are XML based so you can look through them meaningfully in your favourite text editor.) Take for example the creation of the 'Mikrobus-Proto-22' text object, in Corel:
<g >
<g transform="matrix(1 0 0 1 -16881.1 -50490)" >
<g >
<g >
<g >
<g >
<g >
<text font-weight="normal" gorn="0.1.1.1.0.0.0.0.0.0.0" font-family="Droid Sans" id="label" font-size="3529.2" x="65802" y="104855" fill="black">Mikrobus-Proto-22</text>
</g>
</g>
</g>
</g>
</g>
</g>
</g>
Whereas from Affinity:
<g id="label" transform="matrix(1,0,0,1,48920.9,54365)">
<text x="0px" y="0px" style="font-family:'LucidaGrande';font-size:3529.2px;fill:black;">Mikrobus-Proto-22</text>
</g>
Now (again no expert so I might be missing something, but) it would appear that there are many redundant <g > tags each adding to the overall file size. Without them the file becomes much smaller without realistically changing the final product. Well, aside from the change in font as I assume you don't have Droid Sans installed...
Kind of an example of lossless compression (https://en.wikipedia.org/wiki/Lossless_compression)