"만약 당신이 상당한 시간을 해외를 여행하는데 보내지 않는다면 감당하기에 벅찬 일이 될 수 있다."
Unless you've spent a considerable amount of time travelling abroad, it can be a daunting/difficult task to handle.
I think it is fine except for one thing.
The original sentence says "보내지 않는다면", which is in present tense.
So the translation should be "Unless you spend..." rather than "Unless you've spent...".
The sentence matching your translation would be:
만약 당신이 상당한 시간을 해외를 여행하는데 보내지 않았다면...
That's all the nit I can pick with it :-)