list manipulation – How to convert decimals to integers and joint them to a string for exporting

Try

StringJoin[StringTake[StringReplace[ToString[Flatten[Transpose[
  {{a,b,c,d},{0.1,2,0.15,5}}]]],{","->"","."->""," "->""}],{2,-2}],
  "=",ToString[{0.1,2,0.15,5}]]

Start from the innermost nested function, strip that out, run it, see what it does, then look it up in the documentation and see if you can understand why that does what it does and how it gets the input slightly closer to the output that you want, then repeat with each next outer layer.

Then you can export that resulting string to your file.

If you carefully do that then you should greatly improve your skills to be better able to do your next problem.