I can totally empathize with your dilema, I had a lot of misgivings and there are lots of strong opinions on vaccines and it can be a touchy subject, - so this isn‘t an opinion, or advice,
its just my approach :
To my knowledge, (but as always, I stand to be corrected ) the lepto vaccination doesn’t cover all forms of the disease so its hit and miss anyway and the vaccination doesn’t last long so needs repeating fairly often. I‘ve read that there have been cases of serious side effects, - although these probably do have to be put into perspective and its true, one shouldn’t believe everything Google claims. The vets will always advice pro vaccination because they are, understandably, in it to make a living. (I had the same discussions re kennel cough etc)
I had quite an argument with our vet and he finished his lecture with -„ well its your decision“,- and that is it precisely!
So I decided against. My dog is healthy and isn’t compromised by age or any other issues, he gets a healthy diet and so I feel, even if he was unfortunate to get lepto, his immune system would cope.
Unfortunately I have to keep updating Rabies so that we can travel back to UK but apart from the basic immunations as a pup, I haven’t updated anything else. We also live in the country.
I may be right, I may (hopefully not) be wrong but if my dog suffers illness, I prefer to think it was because of an unfortunate but natural cause rather than something which I had instigated.
You can only follow your instinct but don’t allow yourself to be pressured and give yourself enough time to work out what you want to do.