Dear employer,
I've downloaded your sample and de-noised the clip and I'd like to show it to you, no strings attached.
I could help you de-noise the entire 3.5 hours project, no problem. In the other hand, I feel that any honest professional would tell you that the best thing you could do to improve the overall audio quality is to re-record it. It can be done with your smartphone, since most phones have a better mic and better noise-cancelling algorithms than a laptop, making it easier to enhance and de-noise.
Please setup the chat if you'd liketo listen to the clip I've made for you.
Bests of luck!
Ariel S.