I would get it, simply because its often fatal if they contract it.
Definitely give it on a separate day of vaccines, and pre-treat 20 minutes prior with Benadryl (they should do this at the clinic).
I have seen far to many “city dogs” die from Lepto, not because it couldn’t be treated, but because it can be VERY costly to support them through the symptoms of the disease (and some can die of kidney and liver failure).
Its up to you, there are risks to the vaccine and it may be a good idea to discuss with your vet the costs.mortality rates of contracted lepto vs. vaccine reactions.
From my days in GP clinics, I had seen about 2500 lepto vaccines given, no pets died and maybe 5% had mild reactions requiring an additional dose of Benadryl.
Lepto in most cases should be given every 6 months.