I agree with RP’s post. Just wanted to add a couple of comments. The tankless water heater unit will cost from $400-$700. So subtract that from your estimate. It leaves you with $1100-$800. What’s that for? Just for labor, it could be about one or two days work for a Journeyman plumber. But you can bet that there’s more involved. You’ll need vent pipe and fittings, and may need some electric or gas work, requiring more materials. Propably need to do some carpentry as well.
Go ahead and get a couple of other estimates, but $1500 sounds about right. When you subtract the materials cost, you are talking about probably $50-$80 per hour for the labor.
NtP